Can you make Attachments mandatory during Purchase Requisition Approval?

Summary:

For a high value Purchase Requisition, the client requires that there be an attachment attached while submitting the approval.

Content (please ensure you mask any confidential information):

Is there a way to make attachments mandatory only for a certain stage of approval for a Purchase Requisition, where, without attaching, approval is not allowed. I believe if this was done through form customization, then it would get applied for all stages, and we need this to be applied only for high value Requisitions which will require approval from a separate group.

If this is not possible, is there a way to customize the notification template to send a customized template only for a particular group, where we can add a custom information so that the approves ensure they read it and take the necessary action before providing the approval?