Maybe I'm missing something important but it sounds like these two changes make the system call behave more like the documentation. That should be a good thing and a no brainer.
The first change, causing it to actually get busy writing when the call is made but without blocking is kinda what you should have been expecting from explicitly making that call in the first place. The existing kernel behavior of basically ignoring the whole request is the error. If you could live with it getting written eventually when the system got around to it you could have skipped the call and got the same result.
Same for the range. It is actually implementing behavior that has long been documented in the API but left unwritten. Even if you have a bug and are specifying the range wrong you still get the same result you used to get, a write when the kernel gets a spare roundtuit. So all this is doing is increasing the odds that a range that is correctly specified will get written in the case of a crash. It could have happened before though and it might not, and it still might not get written. So all one can say is if you have buggy code it is possible you will get bitten a little more often with this change but probably all that will happen is you won't get as much of an improvement in reliability.