Can I create custom 3d animations from inside a game?

Hi, I would like to do a custom battle game, where players “invent” their own martial arts and customizable moves. Is there a way to create custom 3d animations from inside a game at runtime? For example, the game base character has front kicks and jabs. When they enter a menu, they can see their character model and some “pivots” representing the “bone in the joints.” The players can move the pivots in up to 10 frames and create a custom animation that can be saved as a custom move. For instance, moving up the knee and feet pivot in one frame. In 2-3 frames, move the knee and feet pivot, until the character model does a “side kick”. The frame moves would be interpolated, then, after finishing go back to rest position. Then you can save. Also, I want the player to have complete freedom, even being able to do jump moves or bend the elbows backwards.

How can I do this with UE4, if possible at all?