Through a seasonal peak, do you loosen the target or raise the budget first?

Our booking peak runs from the first week of January to about mid February, and every year I have the same argument with myself in December! Conversion rates roughly double in that window, so the same target CPA is much easier to hit and the campaigns could take considerably more volume than they normally would. The question is which lever to pull. If I raise the budget and leave the target alone, the system should simply take more of the newly available cheap traffic. If I loosen the target as well, I buy volume I would normally reject, at a cost that's only justified while conversion rates are high. Doing both at once feels like a good way to learn nothing. Which one do people move first, and how long before the peak do you do it so the bidding has settled by the time it matters?