I don't mix and match fasteners either. Studs load the cap and block differently from a bolt. It may never be a problem - but doing it will cause stress risers in the block and cap and can distort the cap's main bearing surface. It's similar to torquing one bolt on a head to 200lbs, and leaving the others at 85. SoI figured I'd take the 10 minutes it takes to cut down the stud and use a 12pt nut. BTW - I'm fairly certain .050" isn't enough to fix it...