Sorry for the delay. TL4 users are not able to edit the above wiki post since the topic is closed. As per the code, TL4 users should have the ability to reply to the topic to edit a post in it.
Thanks for the info! It turns out the topic was not closed, but the category was. I moved the topic to a different category that was not closed, and a TL4 user confirmed they were able to edit it.