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.

One definition of "facetious" is " not meant to be taken seriously or literally", or 'ridiculous', so the usage of 'facetious' is not dialectical, or non-standard. the sentence here means:

I am not asking for a ridiculously drastic grade change, just one that would get me passed.

Such usage of words, although not common, is not necessarily non-standard. It may just be unique, or archaic. For example, the word 'discover', can be used to mean 'to find out' as in:

He discovered that John had two covers.

or it could mean, 'to reveal'

John discovered to him that he had two cars.

Your student was asking you to adjust her grade just enough so she passes, not so much that her grade is way out of line. Adjusting a D+ to a C- is a reasonable request, Adjusting a D+ to an A+ would be a facetious request.