I was really surprised at the low costs for modifying the electronics from my Spoiler a couple of years ago - it won't cost you an arm and a leg.
I would ask how much more it would be for adding another filter and Q switch. Also consider getting 3-way Q switches - I recommend 0/3/6 dB.
If your Persuader has a single pre-amp it might be good to have a separate pre-amp per pickup, although that would probably add considerably to the costs.