Dynamically Change Attachment Drilldown

Hello Experts,

We have a requirement to move the Siebel attachment to an external document management system, we will use APIs to read the attachment in base64 format and push it to the external system, but after that, we want to make part of the attachments based on a condition not viewable from Siebel, so the idea we are thinking about is changing the drill down on the attachment file name, to show popup message tells the user to view this file from the document management system, while other files can be downloaded and viewed normally, is this possible? and if not,