UDFs for attaching Word documents or PDFs

Hi Experts.

Our customer has UDFs attached to the Item Master Data screen.

These UDFs are Type = General and Structure = Link.

There purpose is to allow the customer to attach .doc and .pdf files to the Items.

This is working well EXCEPT when they want to change the attachment, eg. if they wish to change the document attached from Document1.doc to Document2.doc.

This does not appear to be possible because the field is greyed out and if they double click on the field the existing attachment opens.

Is they any way around this?

Thanks,

Julie Coppins