In light of all the edits to the question...
In order to forbid trimming the hair of the mustache you would have to assume that it is forbidden due to the prohibition of lo tilbash (loosely: men can't perform "women's" actions and vice versa) and that lo tilbash still applies to shaving despite the fact that the majority of men in the world shave their faces entirely. Alternatively you can hold like the Tzemach Tzedek (YD 182) that all facial trimming is forbidden, at least miderabanan. (I think this opinion still requires the mustache to be considered one of the 5 corners. See next paragraph.) Both of these opinions appear to be minority ones (in my opinion). Also important is to note the Shulchan Aruch YD 390:1 which in discussing the laws of mourning, permits someone during sheloshim to trim his mustache if it is obstructing his eating. Clearly not all mustache trimming is forbidden.
In order to forbid shaving the hair of the mustache you have to assume that the implement you are using to cut with is forbidden to use to shave with (certainly a razor blade; possibly an electric shaver). Also you have to assume that the mustache is one of the 5 corners of the beard that we are forbidden to destroy. The Tur in YD 181 lists two different opinions about what these 5 places are. One opinion, Rabbeinu Channanel's, includes the two "corners of the mustache." The Tur also quotes the Rambam that the entire mustache is not included in the prohibition. It thus seems likely that at least the center of the mustache is not considered a corner.
However, it is important to note the words of the Rosh which are quoted in Shulchan Aruch YD 181:11 that since there are so many opinions about where exactly the corners are, we do not shave anywhere on the beard with an implement that destroys the hair in a forbidden way. I think those words are the strong tradition among Jews and are applicable here as well.
Thus there is certainly room to forbid shaving the mustache with a razor blade (and possibly an electric shaver).
I cannot comment regarding kabbalistic concerns.
[I used the definitions of trimming and shaving brought in the question.]