I like your enthusiasm but i must ask, why?
Should you go through 12 in the first clip, shouldn't the 10 in the next be enough?
Even if this is plausible, would the risk of messing up the 10 rounder be worth it for 2 more bullets in a backup clip?
Either way i hope you get a good answer, and even more success if you find a way to convert the clip. If you have a doubt, don't risk it!