I would let them press my hair, and THAT's going a good lil bit out of my comfort range. I'm not trying to have them do anything to my hair that looks good for the 2.5 hours I'm in the studio with people buzzing all around me, and then I get home and have no clue what to do with it and end up with a torn-up head.
That defeats the whole PURPOSE of a makeover - I'm trying to take that home and incorporate it into my life, not look good for an hour long show on some network.
So. No bleaching. No chemicals, period. I'd let them use heat to press, and I would let them trim as my hair hasn't had a trim in a minute. Cutting me into a 'straight' style - hell no. I'd even let them put a weave in my head - as long as they weren't using glue.
And if the stylist isn't skilled enough to make me over within those guidelines, s/he ain't skilled enough to be in my head. Period.