To answer the first part of the question, no I don't think there's any way of "finalising" any adjustment in LR. Remember that LR merges all the edits anyway. For example, if you increase exposure 0.3, then another 0.3, then 0.5, then -0.3 the result is that LR stores an exposure value of +0.8, the net value.
PS - the history panel stores all the individual steps of course, but also stores the net result of the edits. Only the net result of the edits is stored in the .xmp sidecar file.