I could add something like versions in addition to branches related to UE4 updates.
I don’t think you have to redo your tank for each new version. With BP content you can use migrate function to merge versions or even use BP merge tool ( haven’t tried it myself yet).
With compnent based approach you would only need to merge components that are used in your projects. In some cases that won’t be enough, but that would be a minimum.
For example you could duplicate T-26 for your base setup, keep copy of T-26 as a backup and change models and logic in a duplicate. Later when you want to update, just migrate new version of T-26 into your project. This will bring over all dependencies and components, updating components which are used in your custom BP ( copy of T-26). On top of that you could see all changes done in T-26 Pawn blueprint itself, as sometime it’s not only content of component changes but interfaces/function calls. Those you would need to update manually. The only problem with this approach as far as I see is default values of variables in BP components - if default value is changed in the source of component, it switches custom value to default in each instance of component. Which is a nasty thing, for example you set moment of inertia for the engine to 2000, if I change default value to 200 and merge, you might not spot such change and vehicle will behave differently.