Creating of Modifying Robots

Are there rules for creating or modifying robots? Specifically if I have a player playing a Mr. Handsy are there rules for how to change one of his arms, etc.?

There are rules for modifying a Mr. Handy.

There are rules for installing Robot Mods and different armor. There aren’t rules for changing out say a Buzzsaw arm for a Pincer arm.

You can get different arms during character creation by choosing from the various equipment packages but there aren’t rules for changing them during gameplay.