I'm looking to replace the active EMG's in my guitar with non active S. Duncan's. Is this easy enough for a guitar tech to do? I've never replaced active pu's with non actives before so I wasn't sure if this could be done with little trouble
The only real 'issue' is installing a bridge grounding wire, assuming that your guitar didn't come with passives to begin with.

In general though, it's a like-for-like replacement - remove the old pickups, pots, jack and switches, then drop the new ones in.