Google it bro. It's common practice to back them off and re-torque them.

 

A quick search on Google did not indicate common practice. Rather, I found contradicting opinions as usual.
The elastic transformation of the bolts/head must be an order of magnitude larger than gasket compression upon first warmup. Thus, I suggest any gain from a retorque would be minimal. I am under the impression Mazda does not call for one either. I would be interested to hear of other theories though.