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For Android application ID, change the default Config.applicationid inside android/app/build.gradle.
GraphQL
For any minor changes it would be best to extend the persisted queries as described in the GraphQL documentation, for any changes that are outside the possibilities of the existing schema there are two methods:
The first (easier) way is to create a lightweight plugin that holds the schema and queries you need, and that implements any custom resolver or formatter classes that you will need.
The second (safer) way, is to fork the totara_mobile plugin. This will be a bit of work up front, but it will allow you much more control in the long term, and if the totara_mobile plugin changes your custom app code will still work.
In either case, your queries can alias core GraphQL queries (see /totara/mobile/webapi/mobile/scorm.graphql) or if you need new properties you can implement your own resolvers to extend core (see /totara/mobile/webapi/mobile/course.graphql and the associated resolvers in /totara/mobile/classes/webapi).
TotaraTheme object
TotaraTheme object has the main properties so you can fully customise your app. It can be found in this path: src/totara/theme/Theme.ts
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