In many cases it's useful for users to be able to change software defined tags, especially for tags set by abusefilter. Such tags could be removed by users as a kind of control action. Nevertheless, manual use of software defined tags should be deactivated (on a per-tag base) by default. Furthermore, it shouldn't be possible to activate all tags, software should be able to disallow activation of machine tags by sysops isf this is really needed (I'm not sure if this is really required, because users with managechangetags permission are really trusted users and any changes by users in cases of mistakes by the managechangetags user could be reverted easily because of the tag log) Maybe cases where you want to be able to edit a software tag are nearly the same as the cases where a tag is a problem tag, so maybe the allowactivation (if required) and problem setting could be merged.