Setting messages to delete on iPad but not iPhone.

I still want to be able to send and receive future messages on my iPad but I need to delete old messages to free up space. I do not want to delete them from my iPhone. I want to just change my messages setting to “Keep 30 Days” instead of “Keep Forever”. Will this only change my iPad or do I have to turn off messages in the iCloud first? And if I turn off messages in the iCloud, will all of my devices still continue to receive all new messages?