Pega Constellation: Display a Local Action Only When Assignment is Open (Perform Mode) and Hide in Review Mode

Center-out™ approach (Out of the Box)

This configuration is supported in the model.

I just put this together to answer this question. However, personally, I am not a fan of this UX, appearing/disappearing buttons could lead to some confusion.

DX Component

If you need to place actions, in the context of using the form, then you could use actionable button DX Component.