Where do you obtain your legal facts? I find it hard to believe that only the front two windows need to be 35% when the RTA has a diagram on their web site stating the opposite. This may be the case for utes and vans etc, but not for sedans.

My Uncle was a tinter, but he's stopped now (it is the worst job second only to cleaning septic tanks according to him).
Regarding illeagal tints, the tinter does get fined very heftily if the car owner is stupid enough to drop you in it. And the car owner will also be forced to remove it if caught. If not, don't bother paying insurance premiums on your car, because chances are if the assessor notices the tint and does a simple lux test, then your going to have a big bill at the panel beater as well as any legal action by the other driver.
As for demister lines, sometimes one bar can be taken out as the rear is usually done in two pieces, and if your not EXTREMELY careful with cutting the two pieces across the window, then a line can be cut.
The tint can handle heat fine and it won't bubble with the small amount of heat the demister makes (hot day is worse)
The demister lines will be SHOT by removing the tint and their is no truly effective way of stopping this from happening.

as i said i work as a tinter for a company that has been tinting windows for 25+ years and we get our facts from rta and otherathaurities manuals provided to us by them. the picture on the rta website was a gengral guide only and is about 8 years old as the legislation was changed about five years ago do to some import cars comming to australia where the back screen come standard with frosted tint on them ie silvias. as i said earlier if the custemer wants an elegal tint we will doi it but dont isue a reciept. but we do isue receipts for 35% front and anything else on the back.

I always get my rear windows done in one piece, costs a little more, but worth it (at least in my mind) knowing there will be no serperation or damaged demister wires.

i've only ever seen rear windows done in one piece...

nah mate rear demisters are no probs

as for rego, i had tint on my car at one stage but i had to pull it off cos if had distorted a tiny bit. so depending on where u are, they can be a***hole about tinting in my perspective