Another option is you can add a "User Property" in Firebase like "app_version". Then when the app launches add the following code:
let version = Bundle.main.object(forInfoDictionaryKey: "CFBundleShortVersionString") as! String
Analytics.setUserProperty(version, forName: "app_version")
You can then use this User Property in Remote Config as a condition and voila you can base some Remote Config value of of the version number. Note this will require the use of Firebase Analytics as well.
Adding user property Firebase