@damedus I am slightly confused as to what you are doing:
1) The signing thing I mentioned goes out with the newer kernels that is to say there is a blacklist with each new kernel of previously valid 360s that can no long sign saves, it is usually reserved for those making hacked saves though.
I found the link that explains this all quite well:
http://xorloser.com/?p=45
2) I am not quite following what you are doing.
If I have grasped it though
You have a modded 360 that never touches a network or at never touches an least an external one.
You have the capability of reading and writing the drive via means that are not a 360 (there are loads of different hard drive apps)
Something like:
http://gbatemp.net/index.php?showtopic=137...t=0&start=0
Or do you mean you grab the dashboard updates and downloadable content from a stock 360 using and later swap the hard disk back to the off network 360.
"detect via HD"- if they can detect via an external device and not the 360 itself then we are all screwed. Note however that this has not yet happened, people have also ran scans on hard drives and as far as I am aware no "useful" changes were detected.
My freshly updated 360 (grrr) would seem to indicate MS do not mind the idea of you updating the kernel via this route, DLC is what sets things off in my head.
If you mean stuff like
http://gbatemp.net/index.php?showtopic=137...t=0&start=0 then it is game on as far as MS are concerned.
As for the other DLC I thought it was console locked and while you could transfer ownership (see threads on new 360s/hard drives and what have you) a straight swap like you talk of I am not sure works.
Custom kernel, the recent work with rebooter apps would lead me to believe this is a route that will be explored but I doubt it will become essential, not to mention it will require a homebrew capable 360. I sense you need to read up on how modding the drive works and the 360 security in general:
http://www.youtube.com/watch?v=uxjpmc8ZIxM&fmt=18
You then seem to go onto a rant which needs no comment.
Others a reading of
http://www.xboxhacker.net/index.php?topic=2943.0 might also be in order.
edit: @jaxxster risk sure, high risk I am not so convinced about. I call squeaky wheel/gambler's memory.