Batch Edit Album Art from Progressive to Baseline Support?

[ohrenkino]

See the FAQs/Howtos on how to create an action:

Actions and batch-operations

How to create a new action? First, create a new action group via Actions > [Actions] Actions or Alt + 6. Then, click on the button [New] New and give your action group an expressive name, e.g., "All tag fields Upper Case". This action group can be applied to the selected files after you have added one or more actions to it. Now, you can create a new action in your action group via the button [New] New and choose the desired action type from the list. At the moment the following action types …

and

Export Cover to File – Mp3tag Documentation

Use an action of the type "Export cover to file" to export.
Enter a useful format string like
Format String: %album%_%title%_%cover_type%
Execute the action.

Do the conversion.
See the help on the next action type:

Import Cover from File – Mp3tag Documentation

Create an action of the type "Import cover from file"
Format string: %album%_%title%_%cover_type%.jpg
Tick "Remove existing covers"
Execute the action.
This should be it.