I think it likely that Hellboy himself isn't gonna be bothered by appearances much.
If appearances or manifestations would get to be alterable or limitless then such would mean that any such altering would not have to be as remarkable in itself.
As if even limitedlessness would be bound or restricted by how stuff would be to matter.
Since I think that matters of story present themselves as how or what they'd be essentially, or as how they'd be seeming in the eyes of some or more at least.
It seems likely that Hellboy needs to leave the world of the living in order to be reaching hell.
As if by then any future dwelling would for him be taking place at someplace being not the living world. Rendering any limits or restrictions to that world moot or at least a thing of the past.
As if mortal life would be as remarkable or unreachable for immortals or the dead or the allegorical alike, just as how mortals couldn't really ever reach immortality (without changing into a different beast entirely)?
But yeah, remarkable or limitless or not: I bet it's gonna be looking sweet!
Both for Hellboy, as for matters of story, heck even for hell itself!
I cannot wait. Is that sounding weird a bit? I. Cannot. Wait.