Did you (recently) try that? Even if it works today, I’m quite sure it’s not a future proof way to do this. @htdvisser has been very clear about this:
Also, no downlink also implies no ADR.
And this is bogus:
And, yes:
Of course, but they should not?
Bummer. For ABP, TTN’s answer is clear; see Can I register an ABP device that has fixed DevAddr, NwkSKey and AppSKey? Also beware that the backend network stack version V3 is due, so don’t rely on hacks that work in the current V2…