managing changes during a crucial move

I am managing the relocation of 1500 employees over a 4 month period. These are technical analysts and engineers who have special equipment, labs and intricate private networks in addition to their connections to the corporate LAN and standrad desktop equipment. I have an aggressive schedule and it seems that as soon as we are set with the databases, move dates, seating arrangements or LAN patching, a change is made. What is the best way to handle changes in the middle of a project? I need to come up with documentation for change procedures before we make a mistake amidst the chaos. ANY advice pertaining to this topic would be appreciated.