you can use a script that loops through all materials and does that. if you don't want to do the script method and you don't care about keeping the materials separated you could just create a new material with vertex color enabled and assign it to all your meshes. link to a script that changes all albedo to vertex colors.…
@decorix you can click on the plugins menu (topbar -> edit -> plugins) in toolbag and click show user plugins, it will open a folder where you can put the script. Then the same menu after your reload should show a button to run it. in 4 it looks like below after installing the script, should be similar in 3.