Pretty much! Just create your new object, add the attachment attribute and off you go.
I worry it being that simple as looking at the normal "Attachment" Business Object there are all sorts of attributes on there. I presume some, but not all are required if I create a new "Task Attachment" B.O.
Reference Number -- String
Serial Number -- Int32 (which is also setup as the Is Name field and which I cant copy as "Is Name" only for string fields in the UI)
File Name -- String 2000
Plus also collection to an Attachment Message BO. Presumably because I set the behaviour up to be a "Message Source" ?
The complexity would come if you wanted it be able to be sent as an email the way the normal attachment is. Do you need that?
What about drag 'n drop?
I've logged a call with support on this for clarification :
"I have dropped Task Change onto the Attachment Business Object to create (selecting "Yes") to create the related attribute. I've added the "Add Attachment" optional action to statuses on the Change Task processes. The problem is on saving the attachment from the Task I get an error because the "Change" related attribute has been set to mandatory in the OOTB database version on which our DB is based. So the big question does the Change Attribute need to be mandatory on the Assignment business object and if not what's the approved way to set to non-mandatory. I'm presuming SQL script here as it's greyed out in the UI."