NO, don't increase pellet amounts when you might not be feeding hay. Stopping hay when your rabbits digestive system is used to it on a daily basis, can sometimes result in a gut slowdown and digestive problems. If you were also to increase pellets at the same time, that will just increase the chances that your rabbit may develop digestive problems. If you can, get some hay at the petstore, or sometimes walmarts carry pet products for rabbits, so it would be a little bit cheaper there. Even if you have to stretch the hay to last til you get your other hay, some hay will be better than none. You can increase the amount of greens a little if you need to, to make up for less hay, but you wouldn't want to increase it by a whole bunch, as that could result in soft poop. Better more greens than more pellets.