I think you are talking about composite time signatures, which is where you change signatures during the phrase. It is another way to write how you are thinking of the time, often allowing you to specify how you see the beat falling. Some composers have used this technique to very specifically communicate the feel of the beat they wanted, going so far as to have bars of 1/8 sprinkled through the work, which forces people to hear consecutive downbeats, sort of like you might use if your roommate wouldn't move his feet and you said, "MOVE YOUR FOOT!" (where each word is a downbeat)
Check out Aaron Edgar's video on Composite Time Signatures. He has some other videos in this series that reference Meshuggah specifically.
Polyrhythm is a little deeper than just moving the beat around. What this is really about is hearing more than one pulse at a time. This can be done with composite time as you pose in your question, but just adding up the eighth notes so that they add up to something divisible by the second meter is not necessarily enough to create a convincing polyrhythm. Check out Example Five from the previous video to see a polyrhythm over 7/8. This is 3 bars of 7/8 that he makes work out by using dotted quarters on the bass. This might be what you were referencing, if you combine that with two extra quarters to put a punch at the end, which I would notate in 2/4. So you would have 7/8, 7/8, 7/8, 2/4; and you would just write it out that way, with a new time signature introducing bar 4. This does not add up to 32, but it would definitely be a cool polyrhythm grove.