Rules lawyer question:

Deadeye says I can "spend" a focus in place of a target lock. Adv. Homing Missiles says I need a Target Lock, but I do not technically "spend" it. So does it work?

Yes. See Proton Rockets.

Deadeye is two parts. First, you may treat "Attack (Target Lock)" as "Attack (Focus)". Second, where a card instructs you to discard a target lock, you discard a focus instead. If the card does not instruct you to discard a target lock, you do not need to discard the focus either.

Rules lawyer question:

Deadeye says I can "spend" a focus in place of a target lock. Adv. Homing Missiles says I need a Target Lock, but I do not technically "spend" it. So does it work?

itsthewoo has already answered the question.

Let me put it a different way. If Deadeye only changed what token type you needed to discard to use a piece of ordnance it would still be next to useless as you'd still need usually still need a TL on the target you are trying to shoot.