Can you have a TL on one ship, but use Deadeye to fire a totpedo at another ship using the focus token?

Yes. Deadeye states you MAY treat the "Attack: Target Lock" as "Attack: Focus" meaning that as long as you have a focus token, you can target any enemy ship you want (or target the same ship while saving your target lock for re-rolls). Alternatively, you can choose to spend the target lock anyway, saving you focus for other die result changes.

Hope that helps!