>>34291
It can be a hard effect to see without more texture on the penis model, but I have two potential solutions for you:

-Make a duplicate of the penis model and lock all the bones of the new model to the original. Hide the original model and animate the locked sections f the new one you want to "move" from there. It's how I usually animate a more foreskin like effect or any minor offsets like twitching I don't want to effect my main animation too much

-Another solution is to lock the bone that controls the penis head to a bone two or three bones down the hierarchy, and then animate the bones inbetween. This keeps the head in place while getting a shifting effect