Is it possible to have a default hold code for user-entered AP invoices?

Client has an 'urgent' requirement, whereby all incoming AP invoices would have a certain hold code placed on them. The hold code is the easy part, it's the ask that the process be idiot-proofed which is giving me agida. I don't see any way where we can configure a default hold code, or make the field mandatory.

Also, I need to find a way to update all open invoices with this code as well…

Thanks in advance.