Actually, don't change anything in SHIII while at sea. Only make changes while "In Base". Not even config files just to be safe.
I've lost 4 careers by doing something to the sim that screwed the proverbial pooch. Tempted as I am I leave well enough alone and change or add while in port.
Another idea is to make a backup of your SHIII folder in My Documents, the complete SHIII folder on your C Drive, and SHIII Commander folder. It'll save you headaches if you make the "big" mistake like I have. Best place to save the backups to is an external HDD. Actually backing up the complete C Drive every so often is the best thing to do. Live and learn.