I have successfully lowered neck pockets on 2 tele builds as they were ridiculously shallow and had no other way to lower the action.

Above points should be heeded as with any Gibbo style bridge & tail piece the height adjustment is critical as these usually sit fairly high off the deck anyways compared to a strat, tele, or lowset hardtail type bridge.

Best to check everything other than pickup height before butchering the neck pocket as that is where you can easily go down a path with no way of returning. Even more important if this is a set neck build. On my only set neck G style EX1 build the pickups seemed to sit too low and thankfully they can be easily raised and still look ok.

On my Tele's the job was slow and painful and being bolt on's it was not as critical and therefore more meat (thickness) to work with. I used 80 grit sand paper and cut out a wooden sanding block the same width as neck pocket but a bit longer so that I could grab onto it to sand fore & aft. A sharp chisel was also used around the vertical edges to get things started plus a bit of horizontal work to ensure things were reducing in the same planes.

All up I had to remove between 5mm - 7mm and it took quite a long time but better to go slow and steady than rush in with a router and take too much off. Thankfully I had a Strat style guitar to use for obtaining suitable height reference points otherwise I would still be complaining about both Teles with too high actions and impossible to cure intonation issues too.

Cheers, Waz