Moving the horn/strobe, by itself, isn't a problem. However, the location it's moved to is important. Also, even though the wiring looks to be simple, lengthening the wires or not using wiring practices specifically meant for fire alarm systems can result in the fire alarm system not properly functioning properly.
Just moving the box also requires CYA paperwork, and has hidden liabilities. In many localities, by law, the only ones allowed to move anything in the fire alarm system are licensed fire alarm companies.
Get a hold of the fire alarm company that normally services your building. Have them move it; having them move it will result in fewer headaches in the future.
Douglas Krantz