Don't know what you guys are smoking...the US (of course) was the first to read the qualification/substitution rules "in fine detail" and start interpretting back 12 years ago with the Wherley/Simon M4- scenario. The only way the athletes in the US M8+ status will change is if there is an injury or the US (at some level) decides not to enter the event at the Olympics.
In the first case, there wouldn't be a law suit, USRowing (and the USOC) would approve as well as FISA.
I think you are hung up on the end date of the M4- selection which coincides with the last possible 'nomination date'...and some short hand for the M8+ where it has a blanket statement that selection for non-qualified is the same as qualified except for the end date of the camp.
At the end of that camp the line ups were 'approved' by the nomination committee (which is represented at all levels not just HPC) and somewhat separates/insulates the decision from a single individual (camp coach). Once that lineup went to FISA and they crossed the line, those names are cast in stone. At this point, USRowing is responsible for the individuals on the team until the final roster is sent to the USOC. From now until that date USRowing has to abide by the rules surrounding the removal of an athlete. After that date the USOC has 'jurisdiction'. Maybe "has to" is too strong and "without legal issues" is more accurate.
From FISA's standpoint changes in lineups really surround injury to a athlete and, somewhat new, the prioritization of boats by a country at the Olympics (although prioritization has been discussed from "day one" in conjunction with qualification and alternate athletes). The Executive Council will try to ensure every possible athlete slot gets utilized. I'd venture to say that if for some reason an athlete was removed "outside of injury" from this boat (e.g. - discovery of non-citizenship) that the qualification may be viewed as void and the next placing would be allowed to row in the regatta. There will be some date in a week or two where all countries that qualified boats have to confirm they will use those slots. If a country declines a slot then FISA will take a look at other qualification regatta "runner ups" across all events to fill these seats.
I guess the last possible, but not plausible, change would be for some athletes in the M8+ to double up. So if you want to start a controversy. The eight returns, breaks up into pairs and goes to trials. One of them wins and excepts the position. This would force the US to double up the M2- and M8+ (since I think trials is after the FISA confirmation date) which in turn opens up two additional slots at the Olympics. The FISA Exec Council looks at the results and determines that the event that was the most compeative that deserves those slots is the LM2x....and The USRowing LM2x gets to go to the Olympics.