I have a 200 amp 30 space main breaker homeline panel. I want to remove the 200 amp breaker and make it a 100 amp panel. I shouldn't have any issues with what, should I?

Why are you doing this.

I concur with Chuck. Why would you need to do this?

It can be done with a 100A back-feed breaker but you need to install a breaker hold down.

I can't find a 100 amp 30 space panel anywhere. I don't have a supply house close by and the 100 amp panel that I need to replace is only a 20 space.

Basically, I need more space and I don't want to have to do a heavy-up

So basically you have 100 amp service to the building. And you are just wanting to use the box itself and change out the main to use it for 100 amp

What are you adding that you need more spaces?

Just install a sub-panel or replace the existing with a 30 space 100A panel.

The issue is once you remove the 200 amp breaker from the 200 amp panel, you violate the UL listing of that panel. Therefore your plan is not allowed.

So I concur with Stan, get the proper panel.

Jerro brings up a good point, what do you need to add? The concern is are you sure the existing 100 amp service can handle the added load.