You don't need to retap the threads, open the hole then use the bolts needed to complete the job. Are you mounting the bags back on?
Fasteners is what I do for a living, If you use a black flat, allen or button head bolt then you just went to a 12.9 grade fastener.
If no one can see the bolt and it doesn't have to be flat then just use a grade 8 Bolts have marks on head to id the bolt. SAE is, 3 marks is a grade 5 and 5 marks is a grade 8. If you stay metric then use a 10.9 it will say 10.9 on the head of the bolt.
Make sure you use a prevailing torque lock nut and not a nylon. Also lube the bolt with anti-seize, this will allow great clamping force.
Tighten from the nut side and not the head of the bolt.
Here is the specs for sae bolts.
http://www.raskcycle.com/techtip/webdoc14.html
Good luck.