Steel can mostly be retorqued as much as you wish provided that the parts are cool to the touch at the time.
When a gasket is involved, the procedure is usually to torque once and leave it. Torquing may actually be a long process requiring that the bolts be tightened incrementally in a certain sequence. Some engines may recommend retorquing after the first 20 hours of operation. There are engines with no head gasket too... I suppose they could be retorqued any time they were cool... but again this should not be necessary.
I see torquing a conductor more as a matter of how big a dimple does it need. Once it has that dimple, it has deformed and the pressure will be somewhat relieved over time as the conductor is squished out. Retorquing it will cause the dimple to enlarge. The difference here is that copper and aluminum are much softer than steel.
