90mm brakes are designed to fit 90mm skis. 100mm brakes are designed to fit 100mm skis... and so on.
Most brakes can easily be tweaked out a few mm. if they rub. Often its only the plastic feet that catch a little and the ski edges will shave those off quickly enough.
If you do need to bend them, its often a good plan to put your boot in the binding, then get two pieces of pipe (e.g. bike seat post) and slip these over the legs. Then bend from each side.
For larger bends you may need to dismantle the brakes and use a vice, heat up the bends... all depends on the material. Tyrolias are tough cookies to bend. Pivot/Axial & FKS-style. are thin but brittle - you won't be happy if they break.
As far as DIN settings go, as long as your setting is in the binding range then you shouldn't sweat it too much. I like to be around the 2/3-3/4 mark on a binding e.g. 9 on a DIN12, but I'd happily ski at 9 on a DIN10 binding, all other factors being equal. However, higher DIN bindings often buy you better safety features and/or materials at the same time (more metal, more directions of release, better retention to avoid unnecessary release). Most DIN10 binding have simpler features than DIN12 ones. For that reason a DIN12 binding is possibly a better choice (or even 14/15 depending on the model/brand).