No, it's incompatible if just a few people change their behaviour. To roll out a change to the network you need to get most of the clients understanding both the old and the new protocol, and then when you have a majority you turn on the new protocol.
You just described a whole-network upgrade. I'd call that an incompatible change
The effort to raise the transaction rate limit is the same as the effort to change the fundamental nature of bitcoins: convince the vast majority to upgrade.