Lots of us can do it, but I would suggest finding someone locally and checking out their work carefully. A second problem with the "appeal to luthier's corner" is that the Commercial Users Policy forbids anyone from contacting you regarding this - you have to look through the "Who are You?" sticky at the top of the forum and decide whom you want to contact to see if they will do it, get prices, etc.
Just to clarify, as it's not clear from the thread, you want to replace your jazz neck pickup altogether with a P pickup? I ask, because it kind of sounds like you want to add an additional P pickup in the middle of the two J pickups.
At any rate, this is a simple mod, and any competent luthier or tech could do it. Just make sure they have insurance in case they inadvertently damage something. Either that or make sure they would be willing to repair anything that comes about in the process. (most have heard my sob story of having to refinish an entire guitar that was thrown across my shop by my drill press...
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