Disabling Edit Access to a List Item Attachment?

I have setup a list in SharePoint Online where users are able to create a request (as a list item) and attach a supporting document.

Once this supporting document is attached and the list item is created, I need edit access to that attachment to be disabled. This prevents them from going back to the list and secretly modifying things to the document after submission.

It's a really important feature that we absolutely must have, does anybody know if this can be done?

Thanks