Is there any possible way to take prom pictures at the Modern?

It would be best to contact the museum staff directly...it seems to me that it is likely an arrangement could be worked out ...the grounds there are lovely as is the museum. They have sculptures outside, etc. So it probably depends on what else is going on.

People take them at the Kimbell all the time which is right across the street from the Modern. You might need to pay admission and check with staff before setting up large equipment.