XF 2.2 PDF Attachment Permission Control for Non Admins



I'd like to know if there's a way to set custom permission for moderators such that - they can add attachments to threads but can't delete them.

To explain this further, I'll make a little description below:

The Issue: My forum has threads that are updated from time to time with new PDF documents. Sometimes, the moderator can mistakenly click on the "delete" button for PDF files that are already uploaded and there's no easy way to re-upload them back to the same position (as described here).

Now, I want "a custom permission" that allows them to edit other user's threads (as usual), add new PDFs and Images but can't delete existing attachments.

P.S.:, If this can't be done in any way, can I set a permission to approve attachments deletion before they're executed?