Epic fail with having different model AP's in the same network, but some models need to run on Beta and others on production, but when you upgrade firmware, you have to apply it to every AP in the network
So the only answer is to create another network, replicate all of the settings, client whitelists, etc, put the (MR33) AP's in that new network and apply a later firmware version to it...what a faff, c'mon Meraki sort it out