Is it possible to replace/remove class features using a subclass? My specific goal is to remove the spells granted by the base class and replace them entirely with homebrew spells (which are all just copies of the real spells). I tried creating an empty feature named "Spellcasting" hoping that it would replace the base class' spellcasting so I could just assign spells to the subclass, but the site just spun forever when I tried assigning the subclass to a character.

The campaign I'm planning has a somewhat reworked magic system; all the same spells still exist, but they are mixed around to different classes. Making a homebrew copy of a spell and assigning it to a different class is easy, but taking a spell away from a class seems less so. I can obviously tell my players to ignore the non-homebrew spells, but that makes for a very cluttered interface during spell selection. It might be my solution, though...

No because a subclass, at least made by the builder, cannot change or alter the main class features in any way whatsoever. Rewriting the spellcasting system cannot be achieved by a subclass and would be a reworking of the class instead which is beyond the scope of this site.

Thanks, that's what I was starting to assume  but figured it couldn't hurt to check. Would love to one day be able to create variant classes, but I can work within these limitations for now.