My guild is having a summer break, and I was wondering if it's possible to freeze the DKP system in that period. The reason I'm asking is due to Decay.

The only way you'd be able to do something like this is to make a new system and make adjustments for each character in the amount of their current DKP.

But the Decay does not stop for any reason. The alternative would be to switch to one of the DKP Tax methods, which operate by applying periodic adjustments, and you can disable the tax without it retroactively affecting the standings.