Somehow, the assembler must have a table somewhere according to which it decides to accept or reject an address. Maybe it's in the form of a file you can edit? Or isn't there a switch to turn this feature off?
Another way to do it would be to write the instruction "hand assembled" like

db 075h,096h,000h

which would be equivalent to mov 096h,#0. A byte is a byte is a byte, you know.