why don't you install some plugins, you have plenty of plugins that can do the job you want.
https://forums.alliedmods.net/showthread.php?p=2693455
if you want to make a server that can save the cvar settings, just create server.cfg file inside your \Left 4 Dead 2\left4dead2\cfg Folder
then just put the cvars you want make sure it starts with sm_cvar, for example sm_cvar sv_cheats 1
to make sv_cheats 1 only works for u, I dont think its possible without some plugins