I was trying to replace a humbucker with a 54' tele lead pickup. I didn't fit so well so I had two chances. I could remove some wood from the cavity or I could file the baseplate of the pickup. I decided to do the second option since I didn't want to modify the guitar. The problem it is that when i file the baseplate I had to file the baseplate magnet too. I wasn't too much, 2mm (1/16'') in one corner.
I don't know i this can affect to the sound of the pickup.
Anyway the pickup sounds good, but not great, the problem it is that I don't know if it is because I had filed it, because the guitar it is quite cheap or just because i don't like the sound of the pickup...