How hard is it to change a visor from non-light to a lighted one? i also have a pair from an 06 G6(non-light)

and a lighted from an 06 Impala LTZ 

It is not difficult. The biggest challenge is running the power (and perhaps the ground wire too) from the visor through the headliner and down the A pillar (under the A pillar trim) to the fuse block to get to a power and ground source. The trick is to do all that in a way that you don't tear, stain or ruin the headliner and that it looks factory.

Take your time. Test fit everything.  Lay things out in advance. Consider wearing gloves around the headliner.

The gloves are a great tip Frosty.