Generally it is not that easy.
Typically there will be a bunch of 120V outlets on the same 120V breaker, not all outlets in the same breaker will be in the same "area". Good chance the breaker servicing that outlet will be feeding other outlets all through your RV.
In a nutshell, you most likely will lose at least half of your 120V outlets.
Additionally since RVs have extremely thin walls, they can not use typical home outlets.
Instead a low profile all in one outlet/box combo is used which the 120V wire runs through uncut and the back is pressed against the wire. The back pushes the wire into sharp pins and the pins pierce the insulation of the wire. You would have to cut the wire or cut back the insulation and solder flexible wires that would go to the 12V outlet. Once wire has been cut it will be real hard to undo down the road if your needs change.
The net effect is a lot of work on your part to make this change and you will lose the use of a lot of outlets.
I would recommend simply running new 12V wires as close to your desired location as possible. You can use cabinets, cupboards and so on to run the wire, just have to be a bit creative but it can be done.
BE SURE TO FUSE YOUR HANDY WORK TO THE WIRE SIZE..
