You dont need to open the fuel gauge to add on a outboard solid state voltage regulator. Simply put a piece of electric tape on the back of it to isolate the gauge can and original limiter from ground. The 5 volts from the regulator back feeding into that limiter will not have a path to a fault, is of no consequence.
Take the switched 12 volt wire away from the gauge and route it directly to the added regulator. Mount that added regulator anywhere you want. It doesn't have to be on the back of the inst' panel. There isn't a good spot for it anyway. Hope this helps.
