And even then you aren't retroactively making it more open. You are just now offering an additional, more open license as well as the existing one.
You haven't taken the original license away, you just provided a better default option.
The same weirdly enough goes in reverse as well. You can provide a more restrictive license retroactively even if the rights holders don't consent as long as the existing license is compatible with the new, more restrictive license. i.e. you can promote a work from Apache-2.0 to GPL-3.0-or-later as the former is fully compatible with the latter. However you can't stop existing users from using it as Apache-2.0, you can only stop offering it yourself with that license (but anyone who has an existing Apache-2.0 copy or who is an original rights holder can freely distribute it).
You can retroactively make a license more open, but you cannot retroactively make it more closed.
https://news.ycombinator.com/item?id=10672751