True Polymorphing my warlock temporarily

[Devilizh]

I am really confused about True Polymorph, My warlock's patron is a Devil and it would be awesome to be able to transform myself into a Pit Fiend at level 20 temporary.

My questions are, am I able to maintain concentration while I transformed myself into a Pit Fiend because he has innate spellcasting? Can I revert back to my old self if I transform myself into a dumb creature during the 1hr limit before it becomes permanent?

I understand that I don't have access to my spells if I transform myself, but does that mean that I cannot polymorph myself temporary if I want to? I'm so confused, how does true polymorph works on myself?

[JackPhoenix]

You can keep (or stop) concentration while polymorphed... innate spellcasting has nothing to do with it. However, low-int creature may be too dumb to realize it should turn back... ask your GM what the roleplaying consequences of such transformation are in his game, and if it's considered metagaming to change back before it's too late.