yes, hot gun. It doesn't harm the tank, if you don't exceed.
I put the tank on a clamp, modify with two higher wings. I blew hot air on lower tank part and at the same time slowly I enlarged the clamp.
If you'll do this, you'll had to work bit by bit, with the hot gun e with the clamp.
When finally I put the tank on the frame, it fits right on the front rubber pins, but it was higher on the rear part (consider that the dominator frame in this point is larger than xl, xr and every other model).
then I stop my experiment because in the meanwhile I found a dominator acerbis tank ...
I should create a fixing for the tank in the rear part, modify a seat (shorten and modeled on tank) and modify the fairing panel under seat.
Here all pictures that I did, note that the seat and the fairing panel under seat were of second series dominator (1992-95)
"Semina un pensiero e raccoglierai un'azione. Semina un'azione e raccoglierai un'abitudine. Semina un'abitudine e raccoglierai un carattere. Semina un carattere e raccoglierai un destino."