Can you still boot into a game?
You are using dash 4920. My suggestion for you is, if you can get into Evolution-X RemoteX again (or any other FTP server), to download/backup the file E:\TDATA\fffe0000\music\ST.DB, and then install the stable (a.k.a. newest version of the) audio hack. Granted, there are some disadvantages to this hack (no custom soundtracks in games, which is why I suggested to back up the ST.DB file before installing the hack), but this hack has its good sides: It is probably the safest hack, and then at least you can know that you'll be able to run unsigned code after you return Splinter Cell, so that should resolve your time pressure.
And then if you want to toy with UDE2 more, you can do so without needing the game.
The MechAssault saved game is not required. I used the 007 AUF saved game just as well, and from what I've seen of the Splinter Cell save it seems that game would work just as well. Still, once you have the audio hack installed, I would suggest sometime installing a MechAssault saved game, and a 007 Agent Under Fire save, so that you have the most possible points of entry.