If it's serversided,
package packagenamehere
{
function servercmdmessagesent(%client, %text)
{
if(%text $= "your blocked text here")
{
return;
parent::servercmdmessagesent(%client, %text)
}
else
{
parent::servercmdmessagesent(%client, %text)
}
}
}
activatepackage(packagenamehere);
Clientsided, I don't know. Clientside-mute can provide answers via its code though