iso – How can I guess the specifications of a movie?

To try to identify the correct type of "Mystery Movie" that I bought and mentioned here, I would like to do some tests.

1 – Can I take several photos on the same roll with a different ISO setting on the camera and then see which one works best? (Or do I have to shoot full rolls at different ISO settings?)

2 – Is there any way to "guess" if it is colored or in black and white just by trying different settings on the camera?

The first release I made was processed as black and white and came out very contrasted. I liked the results, but I am curious to try and prove the film since I often buy unbranded / unlabelled films.