You can use any A-pose model and it should work with the existing animation library. You can change the model rest pose with blender or even within godot itself.
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If you want to use the existing animation with your own model, you can import the model(A-pose) and retarget the skeleton. Then, just add the animation library(check Animlib folder) into animationplayer. If you have any problem in retargeting animation in godot, i suggest to check the godot documentation first.