The diagnosis can be the same, after all whether surgery is successful or not it is the same disease, even if it's cured one can't leave the post-op diagnosis blank.
As for the bleeding in the brain it usually is serious, often life-threatening. There can be small hemorrhages with fairly benign causes, but you have to determine the cause to make that assessment, until the origin has been determined (and therefore the risk of it reoccurring) every brain hemorrhage has to be considered as a serious issue, even if it is a small one.

It is quite possible for the pre and post-operative diagnosis to be the same. As far as bleeding in the brain is concerned, it would depend on the location and amount of bleeding. While small bleeds that are not increasing in size are harmless and do not cause any problems, larger bleeds or those causing symptoms or increasing in size are potentially life-threatening.