I don't see the reason to make this change.  The difference is marginal at best, but using a compile-time constant (which I take it PROMISE_RESULT_CHANGE is) is apt to be quicker than using the status variable here (albeit the optimiser may in fact collapse it down to the same thing).  Of course, if we can break out this last line from all three branches of this if/else-if/else (which looks like it should be a switch in any case) to a common result = PromiseResultUpdate(result, status), then that would be cool; and writing it this way makes it easier to see that this is possible; is that your intent ?
(The next stanza's corresponding change is material, in contrast.)