"param" is a "char *" just like "setLocalPlayerName" function argument, so you don't need to convert to int and then to "char *" again.

so, just...

setLocalPlayerName(param);

and the second argument of "addClientCommand" is a int, so you must not convert that void to char, but do it as an int, like this:

addClientCommand("nick", (int)cmd_nick);