grammar - He changes while.....he says/is saying

1) He changes his facial expression while he says...

2) He changes his facial expression while he is saying..

3) He changes his facial expression as he says...

4) He changes his facial expression as he is saying..

Is it possible to use all four sentences in the context decribed below? Would they all mean the same?

A native speaker told me it is possible to use both (while he says/ while he is saying) with no difference in meaning. However, there
is one aspect that seems to be overlooked and makes it little confusing to me. In this situation the context is that I want to describe one situation in one certain video.
I want to describe what happens in one part of the video (that may take 5-8 seconds in total). Therefore I originally expected that only while he is saying would be the only correct choice. Why? Because in the following sentences it works as follows:

Don't call me when I do my homework. INCORRECT

Don't call me when I am doing my homework. CORRECT Here the "calling" happens WHILE something else is happening.

Similarly for my original sentence. He changes (in my context, it just happens once, it is a "one-time" moment) his facial expression while something else is happening (it has duration, it is happening while something else happens during that time).

Therefore I am surprised it is possible to use both while he says/while he is saying. I would expect "while he is saying" to be correct only. Maybe I would use "while he says" if I wanted a simple description of what happens in that part of the video without going into details. At the same time, I am not sure if the native speaker I asked understood what I was after. Is it really interchangeable or would I have to, if I wanted to express the context described above, use "He changes.....while he is saying" ?

Lastly, would using "as" instead of " while" change anything?

Thank you!