update

Assets/HuaweiService/Editor/AfterBuildToDo.cs

         {
             Directory.CreateDirectory(basePath);
         }
-        string sourceFilePath = Application.dataPath + "/HuaweiService/Android/res/Auth/strings.xml";
+        string sourceFilePath = Application.dataPath + "/HuaweiService/Android/res/Auth/strings.txt";
-            File.Copy(sourceFilePath,codePath,true);
+            if (File.Exists(codePath))
+            {
+                string stringsFile = File.ReadAllText(codePath);
+                string appendContent =  File.ReadAllText(sourceFilePath);
+                stringsFile = stringsFile.Replace("</resources>", appendContent);
+                File.WriteAllText(codePath, stringsFile);
+            }
+            else
+            {
+                string appendContent = "<?xml version=\"1.0\" encoding=\"utf-8\"?>"+"\r\n"+"<resources>"+"\r\n" +File.ReadAllText(sourceFilePath);
+                File.WriteAllText(codePath, appendContent);
+            }
         }
     }
     

Assets/HuaweiService/Android/res/Auth/strings.txt

+
+    <string name="google_game_app_id">Replace me</string>
+    <string name="facebook_app_id">Replace me</string>
+    <string name="fb_login_protocol_scheme">Replace me</string>
+    <string name="tecent_app_id">Replace me</string>
+
+</resources>

Assets/HuaweiService/Android/res/Auth/strings.txt.meta

+fileFormatVersion: 2
+guid: fc1d8b78835a04c1899d9c333d7e3d75
+TextScriptImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Assets/HuaweiService/Android/res/Auth/strings.xml

-<?xml version="1.0" encoding="utf-8"?>
-<resources>
-    <string name="google_game_app_id">Replace me</string>
-    <string name="facebook_app_id">Replace me</string>
-    <string name="fb_login_protocol_scheme">Replace me</string>
-    <string name="tecent_app_id">Replace me</string>
-
-</resources>

Assets/HuaweiService/Android/res/Auth/strings.xml.meta

-fileFormatVersion: 2
-guid: 4bd0293cc87d0461c9b7c19039817a34
-TextScriptImporter:
-  externalObjects: {}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: