I think you are unable to do these changes nowadays.
I don't remember the exact date, around may/2018, but Valve blocked some client cvars being changed through the server. (maybe on a listen server will work but on a dedicated one won't)
This was big noticed on L4D2 when people used to force the instructor being enabled to clients.
Example of server output:
Code:
FCVAR_SERVER_CAN_EXECUTE prevented server running command: gameinstructor_enable.
Since the plugin is from 2009, at that time it used to work.
I already have seen some servers that bypasses it, but usually they replace the server.dll/.so file or rollbacks the game version in a .txt/.ini file that can be found in the game folder.
So your client must match your "server version" (most likely none, or few players will join)