OpenStock 2 allows you to turn all of your option products in to OpenStock variants in one click.
Log in to your admin area and go to Extensions > Modules > OpenStock 2 > Edit. Click on the settings tab. Both "Defaults" and "Bulk Create Defaults" are used when bulk creating variants. Choose these and click save. Now, go to Extensions > Modules > OpenStock 2 > Edit again and click the Bulk Create Variants tab. This page should have your defaults you have previously selected (You need to save the settings before clicking this tab).
"Preview" will tell you have many variants will be created but won't actually create any.
For all products that have Has Options - Regular, "Create" will turn these in to OpenStock variants using the defaults you have saved.