rewrite ? heuuu... yes if u want to change the sound of the "original" game, you can, just make backup of old wavs but these new wavs could maybe not be "appopriate" for some others scenarios... if u want to change "original" game sounds, put new wavs (not with same name as the old wav) to original "sound" folder then edit the sound unit section of the "rules.txt" of the "original" folder (give the new sounds to all units u want)
just put new wavs to the "sound" folder of the scenario, then edit rules.txt of the scenario to change unit's sounds.
If it's not clear, download a ToT scenario and look at it, look at the rules.txt (the unit's sound section is at the end of the the rules.txt) but u'll see thats extremely easy to change sounds.
u can find some ToT scenarios in my website
http://eyn.free.fr
PS: If u play web-scenario with ToT u should make this little change:
Backup "original" folder (ie Copy_of_original)
in the "original" folder (not it's backup) delete all *imp.bmp files and all *.spr files: so u 'll desactivate all animations (terrains, units) and the "original" bmp of the civilopedia.
If u want to play ToT games and scenarios with animated units and terrains again, copy all file *.* of the "copy of..." into the "original" folder.