Necro'ing this since I was trying to work out how this field worked too...
I had a look at mass editing too, and basically using pure SQL you can't do it without borking stuff. e.g.
Code:
UPDATE npc_types
SET special_abilities = replace(special_abilities, '1,1','');
will nuke Immune to fleeing- "21,1" and so on. This seems to add a regex replace:
https://github.com/hholzgra/mysql-udf-regexp but I have nfc on UDF's for mysql. Tbh if I ever needed to I would just write a tool to do it programmatically, but a work around would be to dump the table as a text file and use your favourite regex enabled program to work it's magic - sed, or even notepad++, and then re-import.