Not sure I understand your question… do you want the plugin to save a thumbnail but not set it as a post thumbnail, or do you want the bulk scanning tool to only scan posts without a post thumbnail?
If you want the bulk scanning tool to only scan posts without a post thumbnail you can upgrade to the pro version (I offer support there as well), but you should only need to use the bulk tool once for old posts so you can also just use a little patience and let the scan run fully.
Sorry for miscommunication. Yes, we exactly want the same functionality what you told for bulk scanning tool, but not with pro version. Any way thanks for your detailed reply.
