The saved Game is a copy of the original module with extra state information saved in it.
A module, saved game, .erf and .hak are all saved in the ERF file format.
Since the saved game is saved in the same format as a Hak, you can use the hack pack editor that is in the utils folder to open your saved game and replace the script that you want to change. If the hack pack editor complains that the saved game is not a hak you may have to trick it into opening it. in windows you can do that by one of two methods.
1. Right-click on the saved game and select Open with... then browse to the hak editor.
2. Drag and drop the saved game onto the hack pack editor.