Can't answer the UAC one but I've got the camo one down. Lots of people asking about it recently.
Single shot: You apply to one mech and one mech only. It lasts as long as you don't change it. Then it's gone for good and you have to rebuy it. However, you can change the 3 colors freely at any time to any you own, just the pattern must stay the same.
Unlock: You can use and reuse the pattern any number of times to all mechs of one chassis (e.g. all Hunchbacks, or all Catapults) you buy it for. You can switch to another pattern (which you must buy also unless switching back to the default pattern) and this pattern will always be available again for free. But ONLY for mechs of that chassis!
Normally, the unlock is 10x more expensive and only makes sense financially if you use a single shot more than 10 times which would only happen if you like changing patterns a lot or own more than 10 variants of the same chassis (which would seem silly as no chassis has more than 6 unique variants or so). BUT, with the 50% sale, you might want to go ahead with the unlock if you like the chassis and plan on keeping many of them and think you'll want to change the pattern back and forth sometimes.
Edited by TheCaptainJZ, 07 February 2015 - 01:30 AM.