You know I think I misunderstood your problem.
You want the character to stop actually SAYING "not ready yet"? There is an option somewhere in your game options to disable error sounds that will prevent that. Someone else already provided the code for the actual red error text.
Failing that, there's always the old school method of adding disable and re-enable sound into the code it's self. Such as...
Code:
/run sfx=GetCVar("Sound_EnableSFX");
/console Sound_EnableSFX 0
Your code here... /use 10, all that mess
/run UIErrorsFrame:Clear()
/run SetCVar("Sound_EnableSFX",sfx);
That keeps your in-game sound in tact, but prevents the error sounds. I also threw in the removing red error text code as well just for kicks.