Basically only what changes is that in 6-max you have to play looser than in FR, and also you bet and call much more lighter than in FR.
When i moved from FR to 6-handed i studied quite lot of theory before i even did that actual swap to the 6-max. For someone this could be good way, but for someone else really bad way, so i can't say that this is the ultimate truth.
Also i would like to play just one "game" at the time, so i wouldn't mix FR and 6-max.
But hey, this is just my opinion.