Download or subscribe to the Better District Icons mod and take a look at the SQL code therein. I remember there are issues with using UPDATE statements on table IconDefinitions because it is not actually a "table" but is rather what is called a "view" as I recall. Sukritact had to add some extra code-gymnastics to replace original icon designations with the new ones they were adding. There is as I recall in his code commands to delete things from a table called "IconAliases", which is used by the game in creating the actual information the game will use for showing Icons. I also recall he ended up needing to use INSERT OR REPLACE INTO syntax instead of UPDATE syntax.