I was going through wikidata's abuse filters to update uses of deprecated variables, but couldn't save two of the filters[1] because the tags are invalid[2]. It should be possible to rename the existing tag so that existing uses of the tag applied by the filter and new uses can be searched for together
[1] https://www.wikidata.org/wiki/Special:AbuseFilter/30 and https://www.wikidata.org/wiki/Special:AbuseFilter/38
[2] Tag names must not contain commas (,), pipes (|), or forward slashes (/).
The validation that results in this error (tags-create-invalid-chars) was added by @TTO in 2015 in https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/core/+/878523f6225a9d7e39d58398c6ab3cb0a5193ea7%5E%21/#F3 - T20670: Create ability to add / remove tags from edits / actions
This would actually be pretty simple; tag names are only stored in one place - change_tag_def.ctd_name
Proposal:
At Special:Tags, add a rename action
Rename from: any current tag name, regardless of validity
Rename to: any valid tag name
Db impact: a single write to one row of the change_tag_def table (plus log entry)
New log entry: managetags/rename
Required right: managechangetags (or should it be a new right?)
Tagging contributors team per https://www.mediawiki.org/wiki/Developers/Maintainers for product approval