@Jack MThank you for your advice, I really love this forum, and will definally do the oven method!
Did some shell work with my ski boot fitter who has no experience with snowboard hardboot yesterday. We tried to punch out the side and it felt okay at ski shop, but after I got back home, it seems that the shell shrinked back to the original width... According to my fitter, the shell is significantly thicker and harder to heat up (soften up) than racing ski boots. Does anyone know what temperature does the 951 needs for punching? There is just so little info and so little experienced fitters around me.