The simple answer is Yes and No. Yes, as in there's no point any longer on holding back on anything tactically. If you have a tactic, serve, or other shot that the opponent has trouble with, which you've been using sparingly so he wouldn't get used to it, now's the time to use it. Some figure the opponent is expecting it, and so hold back on their best tactic - this rarely ends well, and usually leaves the opponent and viewers wondering, "Why didn't he do that thing that gave his opponent so much trouble?"
No, as in the score doesn't affect the tactics, except that you no longer are holding back. Some believe that at deuce, you should "play safe." That's only true if you are a nervous wreck and can't do your more aggressive shots - in which case you need a trip to a sports psychologist. Of course, if your opponent is a nervous wreck, that might change tactically what you want to do. It works both ways. Under pressure it's usually easier to make an opening shot, where you choose the shot you are doing, than it is to react to an opponent's shot, where there's more uncertainty. So if the high-percentage shot is to attack, then you should attack, even if you are nervous - and the more you do this, the better you become at doing it under pressure.
The simplest way of looking at all this is that the highest percentage tactic at any time is whatever the highest percentage tactic is, regardless of the score.