Is it safe to replace a Furnace pressure switch with a different one?
The documentation for your furnace, calls for a switch rated at 0.90" wc.  Using a switch with a lower rating, means that the switch may be closing without the proper inducer air flow.   

If you called the tech out because the furnace was not working, you may have a problem that was preventing the switch from closing.  By putting in a different switch, the tech might just be ignoring a big problem.  

There are three main reasons that a combustion air pressure switch would not close.


Obstruction/restriction of the air intake.
Obstruction/restriction of exhaust.
Backed up condensate. 


Pressure switches can go bad. However, they are more often than not an indicator of a problem, not the problem itself.  

I'd call the company, tell them your concern, and ask them to send out a different tech to fix the problem.

It's possible that this is a legit remedy, since you say the new switch is only connected to a single port on the unit.  This means that, instead of reading the pressure differential across the inducer. The new switch is reading the difference between the pressure inside the unit, and atmospheric pressure.  I was not able to find any documentation on this type of substitution from Lennox, so I'm not sure if it's an approved fix or not.