well, let's hope you don't have to remount....
if your new boot is 1cm / 10mm smaller you'll only be 5mm or 0.5cm more forward of your old mounting position
this isn't enough to make a real difference in your skis performance ....
so in your case if you want to remain around the center, you have 2 (3) options...
remount the heel and mount it a little bit more forward, (with your new boots being about 10mm shorter then the old ones you'll be riding +5mm of your current position, so +0.5cm from center )
this is slightly forward but i'm quite sure you wont even feel the difference ...
or option 2
remount the toepiece
and bump it 1cm back, with your new boots this will result in you riding at -0.5cm from center, so slightly back, but probably not noticeable, just like the +0.5
don't remount you'll be mounted at +0.5 with your new boots ....
(beware, for remounting option 2, the toepiece,
this -0.5 depends on how much your tech will bump it back, i assumed he'd mount 1cm back from original, if, lets say, he mounts 2 cm back from original you'll be riding at -1.5cm .....)
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