how many times can they be loosened off and re torqued?

 

In theory, infinitely providing they haven't been stretched beyond their yield point or have damaged threads. That said, I vaguely remember something I read a long time ago about tuners not using them more than 5 times because of thread wear but that may have been only referring to the nuts.

 

before you fit them you take a measurement of them and record it, then when you take them out you re-measure them, and providing they are still within the specified tolerance they can be re-used.