You need to have skeletal meshes on same skeleton. Each skeletal mesh should have only (for eg.) left arm, right arm, left leg, torso, head and so on. So split robots into parts all using SAME skeleton.
Then place more skeletons in blueprints (like you doing with character bp) all together on same component.
Then you can replace each single mesh that represents part of body.
Then make code in that character blueprint that handles variants, do not delete and respawn player pawn.
ps.
check unreal marketplace, maybe there is MODULAR character for free, see how it is done.