So when I have that size 9 carbon toed boot that is perfect in the heel but the toes are to tight and the size10 that is good in the toes but the heel is to big I grind the toe out of the size 9. I go inside the boot with a dime size rounded stone bit with a die grinder (used with a compressor) or dremel and grind from the inside of the boot through the inside leather, through the carbon or plastic shell and leave the outside leather to cradle the toes.
Not only have I made more room by taking out the inside leather and carbon but my toes are now cradled by the elastic outside leather instead of the brick wall like carbon shell. This makes a huge difference. You also go from the toes up against the carbon which will never give or break in, to the outside leather cradling the toes which will break in and eventually give the toe extra space (if needed). Below is a set of grinding bits, I use the upper right one in this kit.