What is CLEO?
CLEO is a modification for GTA 3, VC and SA that incorporates separate scripts you can create, into your game, these scripts are almost identical to the MAIN.scm created by Rockstar and run alongside it.
CLEO download: Here
CLEO download: Here
Can I use my save games with an edited SCM?
Unfortunately you cannot since the save game stores mission information, if the save file cannot find the missions in the SCM then it cannot load and therefor results in your game crashing