Yes, my bad, you are right.
For example ...
START "" /WAIT notepad.exe
... will wait until notepad has been closed.
That's the same when starting Mp3tag.exe.
Huh, what was the problem, please?
Ah yes I see, the new still invisible Mp3tag process will be killed immediately.
And the command script takes the next step.
You can look for a running Mp3tag process ... and if exist, then kill it.
pslist.exe "Mp3tag" -e 1>NUL 2>NUL
IF %ERRORLEVEL%==0 (ECHO.Mp3tag is running.) ELSE (ECHO.Mp3tag is not running.)
IF %ERRORLEVEL%==0 (pskill.exe "Mp3tag" 1>NUL 2>NUL)
You can find pslist.exe and pskill.exe from the Sysinternals suite there ...