[niftich]

Yes, it'd be trivial. In fact, this has pretty much happened with every single IM protocol at some point that was subject to reverse-engineering efforts. Here's some history from the early 2000s [1]. Libpurple changelogs are also enlightening.

[1] https://en.wikipedia.org/wiki/Trillian_(software)#History

[ultramancool]

Trivial to break, yes, but also trivial to fix usually. Once the initial RE effort is done, minor obfuscations to the protocol are typically not major harms.