You can set gravity by placing a
trigger_gravity brush over the entire map, but in order to enable grappling hooks, with or without parameters, you must enable them through the server console. If you have SourceMod enabled on your server, you can do this by having a mod/staff member type "!cvar" followed by the cvar you want to change and its parameters in chat. If you own the server, you can also add a .cfg with the title of the map to the server, with the required commands contained within