Do I have to make a new armature for a slightly different character?

I’ve made a base humanoid armature. This character has a hard-surface leg and is not directly compatible with it. It does not need the extra bone between the knee and thigh bone because it’s for organic deformation, and the position of the knee bone is wrong because it needs to be in the center of the rotary mechanism for the hard-surface deform.

What are my options here? Do I have to make a whole new armature, or is there a way to reuse my base armature and just change the the positions of the bones a bit, so that animations made on that armature will still work here?

It’s for a game project, I only use rotations and no scaling when animating.