Use of "facetious"

facetious
treating serious issues with deliberately inappropriate humour; flippant

Most frequent usage follows patterns like being facetious

I'm not trying to be facetious.

or sounding facetious

Well, Mr. Simon, I want to ask you a question which may sound facetious, but I'm dead serious.

You could make a facetious remark or ask a facetious question but it just doesn't make sense to me that changing someone's grade could be flippantly humorous. I can't detect any humour there at all, so I'm giving this the thumbs down.

If it were phrased like this I think it would make more sense:

I hope you don't think my request for a grade change is facetious. I am quite serious.

I find this usage odd. It is normally used with a manner or remark, or with humour: facetious humour is light and playful; a facetious remark is mildly humorous; a facetious person is prone to facetious humour or remarks. Most of the time, I see it used in a negative sense in modern usage: a facetious person often isn't serious enough. In that sense in can be quite close to frivolous:

The play was full of facetious dialogues that lacked depth.

In your example, neither facetious nor frivolous would seem appropriate: why would a change of grade be jocular or light? Perhaps a bit more context would clarify things.

In the construction used, "not an (X) change, just a (Y) one", X and Y are generally points along a single scale, and X is farther out on the scale than Y. I can think of no way that "facetious" and "just allows me to pass" could be placed on the same scale, so I have to agree with the people who say that this usage is improper.