I'm a hobby iOS developer, could you provide a link explaining how you can do this? I seem to remember reading something about Apple enabling this at one time, but I don't remember the reference now.
I've never had to do it, but I know Apple has an official process for transferring apps, and I believe they've even made it easier to do these days than it used to be. Had I the need to do it, I'd probably go looking through the iTunes Connect documentation.
Doesn't apply to iCloud/IAP
IAP transfers fine - iCloud may be another matter.
Did it about 5 years ago, just had to contact apple, they contacted the developer, Boom! It was all done.