I'm doing this from memory. The pressure switch looks at the differential pressure of the orifice that is built into the cold end header box. The reasoning is if the heat exchanger is restricted the differential switch would not make, but a regular vacuum switch would. This is engineered to protect against heat exchanger problems,and the occupants of the building.
Using the wrong, and I do mean wrong, vacuum switch put the building and occupants in danger. Just this fall at our Lennox Dealer Training the FTC stated this type of practice is not to be done. You are taking all responsibility for anything that goes wrong.
Space heaters or motel is a better option than installing a wrong, and this case, a blatantly wrong part even just for temporary.