You create a new folder in the MC \Data\ folder called "Custom Resources" and save your edited xml file inside that, naming it the same, ie, Resource.xml
As long as that file exists, MC will give it priority over the default one, and, when you update MC, the file in the 'Custom' folder will prevail meaning you won't have to do your edits all over again, as the default one will be overwritten.
-marko