How to make previously Unplaceable blocks placeable?

So I've recently been working on a mod that lets you obtain and break illegal blocks in Survival such as: Command Blocks, Structure Blocks, etc. And I was stumped. I made the way to obtain the blocks, but now I need help knowing how to make unbreakable and unplaceable blocks placeable and breakable. Do you have any tips, suggestions, or even ways to do this?