If you decide to retap, you will probably have to go to an 8mm. Nominal pitch is 1.25mm on a bolt you would find at a hardware store, etc. A fine-thread 1mm & 0.75mm pitch is also available. 7mm is an exotic size & would be very hard to find. I don't see a problem with doing this because there's no way you will get this bolt started in a 6mm hole. Would cause a little inconvenience for the next guy though. (will require a 13mm wrench).