If I swap out everything on a stock autococker is it then custom? - Sure! Adding any aftermarket parts would surely make it "custom".
If I change one piece on a stock cocker is it then custom? - As long as the one piece benefits the marker then I don't see why it won't be "custom"!
Do I have to get a anno for it to then be a custom? - You'd still have a bone stock 'cocker with a "custom" anno job!
Do I have to have some milling done to then be a custom? - Depending how unique the cuts are then you truly have a "custom" milled 'cocker!
If I take it completely apart then mail it to Africa, then mail it back and re assemble it is it custom? - I'd be amaze if you get that package back from "Customs".
Now a days it's tough to say what is custom or not, I'm sure most people who owns autocockers will claim that their marker is "custom". The way I see it, if you're marker was purchased bone stock with all original OEM parts then it will be considered as stock.
Now anything you had to piece together, mix match manufacture parts, custom milled, etc, then that would be truly considered custom.
Again this definition can go so many ways, I'm sure we can pick this all day.