Can you attach them and adjust the size...
Can you attach them and adjust the size if you get different boots?
no. they come in 3 sizes which should accommodate the boot sizes per sizing chart, so if you get a medium because you wear a size 8, and then decide to buy a pair of size 11s, they might not fit.
As long as you're not really changing the *size* of your boots, you shouldn't have a problem - as long as the toebox is mostly squarish in shape. I had an older pair of 32 boots that had a rounded toe and the burton caps didn't fit very well.