When I edit a custom command as song command
it seems to have a problem:
All characters became lowercase letters, however video id of youtube is case-sensitive, the link became inaccessible and the command failed to work
You are not using the alias feature properly. Alias is meant to be the command you want to call, in this case !sr would be what you want there. Any parameters, like the youtube URL, would need to be placed in the Message.