Is it possible to setup a custom message notification within the ticket form?

Is it possible to setup a custom message notification within the ticket form?

Hi, 

I'd like to know if it's possible to create a custom message that will be triggered by a certain action from within the ticket form. To be specific, I would like a notification similar to  the attached that would come up if the agent is changing the Account Name associated with a contact, while still logging the ticket. Since contacts cannot be associated with multiple accounts, this could be the only way to prevent such mistakes.
Custom notification from the ticket form
Is this possible through a custom function? I would like a way to notify the user immediately as soon as he changes the Account Name, before he saves the ticket. We have dummy contacts they can use for the multiple account restriction but they NEED to be notified before they cause record discrepancies with such changes. Any notification is fine - be it from the ticket form, chat, a pop up box etc.

Please advise, I need this urgently.

Thank you.
Jordanne