Yes you can.
I think one thing that demonstrates how seriious the problems with v8 are is that eM Client themselves have posted a guide here in their knowledgebase. The real issue is losing the ability to get at a saved database once it’s migrated from v7 to v8. It’s probably lost unless you made back-ups of the v7 version.
(Personally I just use eM Client to manage an online account with all settings on server, so nothing much to lose for me - I can just re-sync the data to the new installation.)
I’ve also tried to spell out how I did a clean install once or twice on this forum. See here for the most comprehensive. I hope you can find a suitable Nederlandse version of v7 to reinstall.