MIM Telecaster for Epiphone Custom Shop SG 1966 reissue, assuming both are in equal/great condition?
depends. do you like what you are getting? ask to test the sound of it first, make sure that its what you want.
In my opinion? No, I would not make that trade.

The Tele is infinitely more upgradable, the Epi, not so much.

Case in point: I sold a MiM Tele last year that had an Anderson neck, Fralin pickups, cbs pots, switchcraft, a callaham bridge, sperzel locking tuners, and a world class assembly/set-up.

It went to a friend for about a grand.
And that was a VERY friendly price...

If you can get an Epi SG even NEAR that value, I'd like to see it!

THAT SAID: It all boils down to what you LIKE!