diff --git a/.changeset/cuddly-timers-sin.md b/.changeset/cuddly-timers-sin.md
new file mode 100644
index 000000000..1cb781b8d
--- /dev/null
+++ b/.changeset/cuddly-timers-sin.md
@@ -0,0 +1,5 @@
+---
+'@lion/ui': patch
+---
+
+LocalizeManager: added `allowOverridesForExistingNamespaces` option to `constructor` argument to allow for changing data in a namespace for a given locale
diff --git a/packages/ui/components/localize/src/LocalizeManager.js b/packages/ui/components/localize/src/LocalizeManager.js
index 959ffdb43..43dd39814 100644
--- a/packages/ui/components/localize/src/LocalizeManager.js
+++ b/packages/ui/components/localize/src/LocalizeManager.js
@@ -18,6 +18,7 @@ export class LocalizeManager {
     autoLoadOnLocaleChange = false,
     fallbackLocale = '',
     showKeyAsFallback = false,
+    allowOverridesForExistingNamespaces = false,
   } = {}) {
     /** @private */
     this.__delegationTarget = document.createDocumentFragment();
@@ -28,6 +29,9 @@ export class LocalizeManager {
     /** @protected */
     this._showKeyAsFallback = showKeyAsFallback;
 
+    /** @private */
+    this.__allowOverridesForExistingNamespaces = allowOverridesForExistingNamespaces;
+
     /**
      * @type {Object.<string, Object.<string, Object>>}
      * @private
@@ -199,17 +203,29 @@ export class LocalizeManager {
    * @param {string} locale
    * @param {string} namespace
    * @param {object} data
-   * @throws {Error} Namespace can be added only once, for a given locale
+   * @throws {Error} Namespace can be added only once, for a given locale unless allowOverridesForExistingNamespaces
+   * is set to `true`
    */
   addData(locale, namespace, data) {
-    if (this._isNamespaceInCache(locale, namespace)) {
+    if (
+      !this.__allowOverridesForExistingNamespaces &&
+      this._isNamespaceInCache(locale, namespace)
+    ) {
       throw new Error(
         `Namespace "${namespace}" has been already added for the locale "${locale}".`,
       );
     }
 
     this.__storage[locale] = this.__storage[locale] || {};
-    this.__storage[locale][namespace] = data;
+
+    if (this.__allowOverridesForExistingNamespaces) {
+      this.__storage[locale][namespace] = {
+        ...this.__storage[locale][namespace],
+        ...data,
+      };
+    } else {
+      this.__storage[locale][namespace] = data;
+    }
   }
 
   /**
diff --git a/packages/ui/components/localize/test/LocalizeManager.test.js b/packages/ui/components/localize/test/LocalizeManager.test.js
index 00b0b0cae..5b750641d 100644
--- a/packages/ui/components/localize/test/LocalizeManager.test.js
+++ b/packages/ui/components/localize/test/LocalizeManager.test.js
@@ -155,7 +155,7 @@ describe('LocalizeManager', () => {
       });
     });
 
-    it('prevents mutating existing data for the same locale & namespace', () => {
+    it('prevents mutating existing data for the same locale & namespace when "allowOverridesForExistingNamespaces" option is not given in constructor', () => {
       manager = new LocalizeManager();
       const { storage } = getProtectedMembers(manager);
 
@@ -169,6 +169,23 @@ describe('LocalizeManager', () => {
         'en-GB': { 'lion-hello': { greeting: 'Hi!' } },
       });
     });
+
+    it('allows mutating existing data for the same locale & namespace when "allowOverridesForExistingNamespaces" option is set to "true" in constructor', () => {
+      manager = new LocalizeManager({ allowOverridesForExistingNamespaces: true });
+      const { storage } = getProtectedMembers(manager);
+
+      manager.addData('en-GB', 'lion-hello', { greeting: 'Hi!' });
+
+      expect(storage).to.deep.equal({
+        'en-GB': { 'lion-hello': { greeting: 'Hi!' } },
+      });
+
+      manager.addData('en-GB', 'lion-hello', { greeting: 'Hi!', alternative: 'Hello!' });
+
+      expect(storage).to.deep.equal({
+        'en-GB': { 'lion-hello': { greeting: 'Hi!', alternative: 'Hello!' } },
+      });
+    });
   });
 
   describe('loading via dynamic imports', () => {