Hello, friends. Can you unlock class features on D&D Beyond without leveling up? In other words, say I have a third level rogue, but the DM decides I can have a class feature available at 7th level or something. Is there a way to do that? 

There is no way to do that outside of some creative homebrewing (say a custom subclass or maybe a feat)

Can I create custom feats that will show up on a character sheet? 

Of course, there wouldn't be much point to homebrew feats if they couldn't show up on the sheet.

Which class feature is your DM giving you early access to?

I've just started using D&D Beyond, so I am not sure how all of it works. I'll poke around. Thank you. 

You might be able to make a homebrew magic item that gives you the class ability