On ptwiki, there are two similarly named tags (one of them created by accident, I think). Initially, the page Special:Tags displayed the following info about them:

• "Internetês ou miguxês": the "deactivate" link was visible, and the tag was "Applied manually by users and bots"
• "internetês ou miguxês": none of the links were visible, and the tag was "Defined by the software"

After I changed filter 120 to use "Internetês ou miguxês" instead of "internetês ou miguxês", and went back to the special page, it displayed the following:

• "Internetês ou miguxês": the "deactivate" link was visible, and the tag was "Defined by the software" and "Applied manually by users and bots"
• "internetês ou miguxês": the "delete" and "activate" links were visible, and the tag was "No longer in use"

When I tried to undo my test on filter 120, I got:

One or more of the tags you specified is not valid. Tags should be short, they should not contain special characters, and they should not be reserved by other software. Try choosing a new tag name

How can I (or why can't I) restore the filter to its previous state from before my test edits? (that is, make it apply the tag "internetês ou miguxês" instead of "Internetês ou miguxês")

(BTW: is anyone aware of any workaround to T89217: Should be possible to rename or merge change tags?)