Since I now found a satisfactory solution, thanks to Boroda74's help and his
Additional_Tagging_and_Reporting_Tools
http://musicbee.wikia.com/wiki/Additional_Tagging_and_Reporting_Toolshttps://getmusicbee.com/forum/index.php?topic=3833And the - Advanced Search & Replace tool in there, I thought I'd document it here as well as it might help others.
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I created a custom preset that (by default, but easily switchable as needed) looks for value 1 and replaces it with value 2, and correctly handles multi-values & separators too.
So, in ASR (= Advanced Search & Replace):
Enable <Tag 1> (as 'Genre' for my use case)
Enable <Custom text 1> (in the preset rules) - and add a default value if you wish, eg "Bass Music; Dubstep;"
Enable <Custom text 2> (in the preset rules) - and add a default value if you wish, eg "Bass Music; UK Garage; UK Funky;"
In the preset rules, fill out
FieldName : "value" [without the " ]:
Step 1:
Search for: "\@1"
Replace With: "\@2"
This will look for <Custom text 1> in the files selected defined field, and replace it with <Custom text 2>.
Then preview & apply if it is as expected and multi values will get injected with separators corectly.
Also, more info from boroda74, which as well might help someone as I struggled to find the correct variable names in ASR:
"$1", "$2", etc. can be used *only* for captured substitutions, not for searching. for example: search for "^acdc(.*)", replace by "dcac$1", then "acdc2" will be replaced by "dcac2".
Churs.
c.