It is strongly recommended to add labels or explanations in each future version to clarify whether it is a mandatory upgrade (involving consensus modifications), in order to avoid hard forks caused by farmers not upgrading.
We don’t generally have hard forks within the same network version though. We do announcements when upgrade is required, but the default expectation is for farmers to upgrade to new release when it comes out, those who don’t do it on their own risk and may be left behind.