Re: flashing back
If Microsoft can detect drive firmware, and you flash back to original - they will see you have the original firmware on your drive.
If the Xbox 360 constantly checks to see if the drive is flashed and it suddenly detects the original firmware on it again, will Microsoft decide not to ban you now? I don't think so.
If Microsoft only checks to see if your drive is flashed at certain times (i.e. during system updates), they will most likely flag your console to get banned during the next ban wave. If you flashed back to stock firmware during each update - you will avoid this. If not - you will most likely get banned.
If iXtreme LT truly is safe on XBL as long as your backups are good - you have nothing to worry about.
Basically, no one here can answer your question with 100% certainty - maybe c4eva, or people who have connections with Microsoft.