diff --git a/index.html b/index.html
index eed3b34..18d2808 100644
--- a/index.html
+++ b/index.html
@@ -86,6 +86,9 @@ <h1 class="app-title">Firegen</h1>
       <textarea id="bash-import-textarea" class="modal-textarea" rows="15" placeholder="Paste firewall-cmd commands here...&#10;&#10;firewall-cmd --permanent --zone=public --add-service=http&#10;firewall-cmd --permanent --zone=public --add-port=8080/tcp"></textarea>
       <div id="bash-import-status" class="modal-status" hidden></div>
       <div class="modal-actions">
+        <label class="toggle-label">
+          <input type="checkbox" id="bash-import-merge"> Merge
+        </label>
         <button id="bash-import-submit" class="btn btn-sm">Import</button>
       </div>
     </div>
diff --git a/js/app.mjs b/js/app.mjs
index c02900b..6bfd6d4 100644
--- a/js/app.mjs
+++ b/js/app.mjs
@@ -82,10 +82,12 @@ function init() {
       btnImport: document.getElementById("bash-import-submit"),
       btnCancel: document.getElementById("bash-import-cancel"),
       status: document.getElementById("bash-import-status"),
+      mergeCheckbox: document.getElementById("bash-import-merge"),
     },
     (yaml) => {
       editor.setValue(yaml);
-    }
+    },
+    () => editor.getValue()
   );
 
   // Export
diff --git a/js/import-export.mjs b/js/import-export.mjs
index 52af539..6be95f6 100644
--- a/js/import-export.mjs
+++ b/js/import-export.mjs
@@ -2,6 +2,156 @@
 
 import { parseCommands } from "./reverse-parser.mjs";
 
+/**
+ * Deduplicate an array using a key function.
+ * Preserves order, keeps first occurrence.
+ */
+function dedup(arr, keyFn) {
+  const seen = new Set();
+  return arr.filter((item) => {
+    const key = keyFn(item);
+    if (seen.has(key)) return false;
+    seen.add(key);
+    return true;
+  });
+}
+
+/**
+ * Key function for port objects ({ port, protocol }) or plain strings.
+ */
+function portKey(p) {
+  if (typeof p === "object" && p !== null) {
+    return `${p.port}/${p.protocol || "tcp"}`;
+  }
+  return String(p);
+}
+
+/**
+ * Key function for forward-port objects.
+ */
+function forwardPortKey(fp) {
+  return `${fp.port}/${fp.protocol || "tcp"}/${fp.to_port || ""}/${fp.to_addr || ""}`;
+}
+
+/**
+ * Key function for string values or objects with a .value property.
+ */
+function stringKey(v) {
+  return typeof v === "object" && v !== null ? String(v.value) : String(v);
+}
+
+/**
+ * Serialize a rich rule object to a comparable string.
+ */
+function richRuleKey(rule) {
+  return JSON.stringify(rule);
+}
+
+/**
+ * Merge two zone objects. Arrays are concatenated and deduplicated.
+ * Scalar values (target, forward, masquerade) from incoming overwrite existing.
+ */
+function mergeZone(existing, incoming) {
+  const merged = { ...existing };
+
+  // Scalars: incoming wins
+  if (incoming.target !== undefined) merged.target = incoming.target;
+  if (incoming.forward !== undefined) merged.forward = incoming.forward;
+  if (incoming.masquerade !== undefined) merged.masquerade = incoming.masquerade;
+  if (incoming.icmp_block_inversion !== undefined) merged.icmp_block_inversion = incoming.icmp_block_inversion;
+
+  // Array fields with their dedup key functions
+  const arrayFields = [
+    ["interfaces", stringKey],
+    ["sources", stringKey],
+    ["services", stringKey],
+    ["ports", portKey],
+    ["protocols", stringKey],
+    ["source_ports", portKey],
+    ["rich_rules", richRuleKey],
+    ["forward_ports", forwardPortKey],
+    ["icmp_blocks", stringKey],
+  ];
+
+  for (const [field, keyFn] of arrayFields) {
+    const a = existing[field] || [];
+    const b = incoming[field] || [];
+    if (a.length > 0 || b.length > 0) {
+      merged[field] = dedup([...a, ...b], keyFn);
+    }
+  }
+
+  return merged;
+}
+
+/**
+ * Merge two direct blocks. Arrays are concatenated and deduplicated.
+ */
+function mergeDirect(existing, incoming) {
+  const merged = {};
+
+  const chainKey = (c) => `${c.ipv}|${c.table}|${c.chain}`;
+  const ruleKey = (r) => `${r.ipv}|${r.table}|${r.chain}|${r.priority}|${r.args}`;
+  const ptKey = (p) => `${p.ipv}|${p.args}`;
+
+  const eChains = existing.chains || [];
+  const iChains = incoming.chains || [];
+  if (eChains.length > 0 || iChains.length > 0) {
+    merged.chains = dedup([...eChains, ...iChains], chainKey);
+  }
+
+  const eRules = existing.rules || [];
+  const iRules = incoming.rules || [];
+  if (eRules.length > 0 || iRules.length > 0) {
+    merged.rules = dedup([...eRules, ...iRules], ruleKey);
+  }
+
+  const ePt = existing.passthroughs || [];
+  const iPt = incoming.passthroughs || [];
+  if (ePt.length > 0 || iPt.length > 0) {
+    merged.passthroughs = dedup([...ePt, ...iPt], ptKey);
+  }
+
+  // Preserve rule_groups from existing (import never produces them)
+  if (existing.rule_groups) {
+    merged.rule_groups = existing.rule_groups;
+  }
+
+  return merged;
+}
+
+/**
+ * Deep-merge two firewalld config objects.
+ * Zones are merged per-zone. Direct blocks are merged.
+ * Top-level keys from existing that aren't in incoming are preserved (e.g., variables).
+ */
+export function mergeConfigs(existing, incoming) {
+  const merged = { ...existing };
+
+  // Merge zones
+  if (incoming.zones) {
+    if (!merged.zones) merged.zones = {};
+    for (const [name, zone] of Object.entries(incoming.zones)) {
+      if (merged.zones[name]) {
+        merged.zones[name] = mergeZone(merged.zones[name], zone);
+      } else {
+        merged.zones[name] = zone;
+      }
+    }
+  }
+
+  // Merge direct
+  if (incoming.direct) {
+    if (merged.direct) {
+      merged.direct = mergeDirect(merged.direct, incoming.direct);
+    } else {
+      merged.direct = incoming.direct;
+    }
+  }
+
+  return merged;
+}
+
 /**
  * Download a string as a .yaml file.
  * @param {string} content - YAML string to export
@@ -53,10 +203,12 @@ export function setupImport(fileInput, onLoad) {
  * @param {HTMLButtonElement} elements.btnImport - the import/submit button
  * @param {HTMLButtonElement} elements.btnCancel - the cancel/close button
  * @param {HTMLElement} elements.status - status message area
+ * @param {HTMLInputElement} elements.mergeCheckbox - merge toggle checkbox
  * @param {function} onImport - callback(yamlString) when import succeeds
+ * @param {function} getEditorYaml - returns current editor YAML string (for merge mode)
  */
-export function setupBashImport(elements, onImport) {
-  const { btnOpen, modal, textarea, btnImport, btnCancel, status } = elements;
+export function setupBashImport(elements, onImport, getEditorYaml) {
+  const { btnOpen, modal, textarea, btnImport, btnCancel, status, mergeCheckbox } = elements;
 
   function openModal() {
     textarea.value = "";
@@ -116,7 +268,24 @@ export function setupBashImport(elements, onImport) {
       return;
     }
 
-    const yaml = jsyaml.dump(config, { lineWidth: -1, noRefs: true });
+    let finalConfig = config;
+
+    // Merge mode: combine with existing editor content
+    if (mergeCheckbox && mergeCheckbox.checked && getEditorYaml) {
+      const existingYaml = getEditorYaml();
+      if (existingYaml && existingYaml.trim()) {
+        try {
+          const existing = jsyaml.load(existingYaml);
+          if (existing && typeof existing === "object" && !Array.isArray(existing)) {
+            finalConfig = mergeConfigs(existing, config);
+          }
+        } catch {
+          // Existing YAML is invalid — fall through to replace mode
+        }
+      }
+    }
+
+    const yaml = jsyaml.dump(finalConfig, { lineWidth: -1, noRefs: true });
     onImport(yaml);
     closeModal();
   });