Yep, it blacklists, if the plugin crashes while validation. You can edit the blacklist by using a sqlite editor. You can find the blacklist database by selecting the help menu in Renoise and then choosing “show preferences folder”. The blacklist file is named “CacheFailedPLUGINTYPExxx.db”. I usually use the freeware “DB browser for sqlite” to open it.
Or just delete the blacklist file. But don’t forget to do this while Renoise is not opened.