Q: Can you reduce the amount of memory Exchange is allowed to use on a physical server?

A: Yes

Sometimes customers wish to use certain hardware for installing the Exchange Server application that already has a specific amount of RAM in place, and that RAM is not within the current recommended  range for Exchange. Can you make this change at the hardware level and not have to take out the RAM? Yes, you can use the boot parameters to adjust how much memory is presented to the Windows Operating System.