go to C:\Documents and Settings\yourname\My Documents\SH4\data\cfg\SaveGames\ find the save game you wish to edit
theres 2 files you need to edit
one is Careertrack.upc just open it up with notepad do searches for you boats original name, then change it to you new boats name, the other is ActiveUserPlayerUnits.UPC
ActiveUserPlayerUnits.UPC looks alittle like this
[UserPlayerUnit 1]
ID=Porpoise
NameDisplayable=Porpoise
UnitName=USS Perch <<< rename the sub here. ex: USS SupremeSubwithcheese
theres another folder called UPCInitial open this and you'll find files of the same name change these also if you dont have a UPCInitial folder in the saved game folder don't worry about it your done
I recommend setting these files to read-only because SH4 has a habbit of undoing your changes. once you save ingame you don't have to worry about renaming it again. unless you make a new career.
The above info was found here:
http://forums.ubi.com/eve/forums/a/t...185#4971074185