I do both electronics/hardware upgrades and modifications - including pickups, crazy wiring set ups, new tuners, etc.
It could be as little as installing Orange Drop Capacitors! for about $10, You get a set of new caps for your Les Paul. May be a minor upgrade, but I know artists such as Slash swear by them!
Here I'll show you my latest upgrade, I put new pickups in this '11 Epiphone Custom Shop Les Paul Traditional Pro.
Here's the victim! I start by opening the control cavity and unsoldering the 8 leads from the volume toggles, and removing the pickups one at a time. I unscrew the bridge pickup, and replace it. Then I re-wire it, to the push-pull toggle. (Man, those connectors were small...) Repeat with the neck pickup, and we're good to go! What an improvement, they sound great with my JCM 2000!
