You can apply the Mp3tag Filter with the Filter expression:
NOT GENRE HAS "24 bit"
If you want to hard code the different cases into Mp3tag Scripting Language, then you may use this proposals ...
For GENRE as single value ...
$ifgreater($strstr(%GENRE%,'24 bit'),0,'do nothing','do something')
For GENRE as multi value ...
$ifgreater($strstr($meta(GENRE),'24 bit'),0,'do nothing','do something')
Detect, whether a tag-field is a multi value tag-field or not ...
$if($neql($meta(GENRE,1),),'IsMeta is TRUE','IsMeta is FALSE')
Combined ...
$if($neql($meta(GENRE,1),),$ifgreater($strstr($meta(GENRE),'24 bit'),0,'do nothing','do something'),$ifgreater($strstr(%GENRE%,'24 bit'),0,'do nothing','do something'))
DD.20110904.1050.CEST