R2API.Animations is a submodule assembly for R2API that allows mod creators to modify existing RuntimeAnimatorController at runtime.
You can add states (both clips and blend trees), transitions and parameters.
When imported into Unity, adds an option in context menu Create/R2API/Animations/AnimatorDiff. In AnimatorDiff you specify Source Controller which is used as base for the diff,
and Modified Controller which should have all things that Source Controller has (recommended just select controller in hierarchy and pressing ctrl + d to duplicate it) + your modifications.
After that you add the AnimatorDiff to an AssetBundle and in code you can create an instance of AnimatorModifications with AnimatorModifications.CreateFromDiff().
BlendTrees.AnimatorDiff that you can create inside editor and load at runtime.NewStates and NewTransitions dictionaries are now lists