There are two risks. One is that you caused a little chip or crack in the glass (not just the coating), and then there is nothing you can do but replace it. The other risk is enough deposits of water, oil, grease, whatever, that the glass heats at a dissimilar rate where the deposit is, also causing cracking.
If there is something to clean off, like fingerprint oil, even a wipe with a dry paper towel will work (unless it's dried on *goop*), but if it is already chipped, it will break anyway as stated above.
The tip does not matter as much as the rest as far as a deposit on it, but do clean it off to take no chances.
Cramped space? Take the bulb out and clean it. Put it back in, wearing gloves so no fingerprint oil gets on. I like thin, nitrile gloves.
However, if there is a chance that it chipped or cracked, then I would plug it into the power connector and turn it on for ~10 seconds as a test before reinstalling it into the headlight housing (obviously, letting it cool down again first), because if it is going to crack apart, it is then a real pain to get pieces of glass out of a headlight housing.