Be very very careful. I say this for several reasons: -
(1) There are several metric bolt standards, those which you're most likely to meet are "8.8" (which is the most likely on an aircraft) or "10.9" (which is more brittle, but occasionally used in a few aircraft applications).
(2) These standards are based upon the material specification alone, and not the quality.
(3) It was a French idea!
One GA manufacturer of my acquaintance, buys 8.8 bolts for a great many applications - but it then has them cadmium plated, de-embrittled, and then batch tests them to destruction. Finally, they get issued with a CofC. The problem is that the head markings are the same, and after a hundred hours on the aircraft you can't see the surface differences between that and an unmodified bolt.
Another uses standard 8.8 bolts, with only a visual inspection, but then puts a very low hours life on them.
I recently saw some new bolts which *I think* were from the Ukraine (Antonov and their many offshoots), and were interchangeable with standard 8.8 hardware but obviously of an equivalent standard to AN.
So, in summary metric bolts are a minefield, and I'd be very careful, even if the head markings match up - two apparently identical bolts may well not be.
G