Since when did hotels have a policy that you have to be a guest to check a bag with them? I've never heard of such a thing actually being enforced.
Regarding trying to check it at MoMa, that would
seem to be a non-starter:
Checkroom
All bags are subject to security inspection before entering the Museum. The Museum requires visitors to check backpacks of any size, shopping bags, and bags 11 x 14 inches (28 x 35.5 cm) or larger. To avoid a lengthy wait in the checkroom line, visitors should not bring such items. The checkroom will not accept laptops or luggage of any size. The Museum reserves the right to refuse other items and is not responsible for items held by the checkroom.