I found this blog post which includes an engine version downgrade script. I discovered that it actually works most of the time, even with blueprints. Most of the assets will become visible within previous engine versions.
It is then required to right-click or bulk select the assets right-click, and resave; with blueprints one can do the same, or open the blueprints and recompile/save. Tested with several engine versions. Just change a variable or two within the python downgrade script, as noted in the instructions: