I remember Slide for Reddit allowed you to choose who to comment as before doing so.
Does this exist for Lemmy yet?
Eternity does
Voyager will get this feature in the next few days!
Summit lets you switch user from most pages, so I can switch user when reading these comments but not actually while typing the comment
Think Eternity can do it
~~Sync ~~did support it, now you need to be in the account that you wanted to reply as before hand.
Play store link: Sync for Lemmy
You need to be in the account you want to use before opening post.
You are correct change who you are posting as at commenting time, is not a feature.