I've been running Wedge with R7-T1

I really like this combo, but can I use the droid action if I already have a TL on the defender to acquire it again on the same ship and get the free boost?

no. You cannot get a target lock on a ship that you already have a target lock on.

However, when shooting you MAY opt to spend said target lock and reroll zero dice.

EDIT - I believe in the FAQ it says that you MAY - so I think you have the option to skip the TL portion

You CANNOT acquire a target lock on a ship that you already have a target lock on. As Crabbok said, you CAN spend it to reroll zero dice. BUT, in the new FAQ, it says that you DO NOT have to acquire the target lock to use the boost action, as long as you are in the opponent's firing arc at Range 1-2.

Ah cool! Great help guys thanks