In a general sense, follow SWAT deploy guidelines.
More specifically, we will endeavour to SWAT only those changes needed to enable, disable, or reconfigure a feature. However, sometimes there'll be the need to SWAT a fix for a critical bug. The criticality of bugs will be assessed case-by-case by at least the Tech lead but the following should make it easy for anyone to assess.
A critical bug is one that meets the SWAT deploy guidelines and causes either a stable feature or one or more wikis to become unresponsive or unusable. If the feature is in beta or alpha, then we likely won't consider the bug critical.
A design change should be SWAT deployed if it falls under any of the following categories:
Visual issue If the visual regression or a fix interferes with the function or a workflow of a feature it can be considered critical
Exception note: if the visual issue occurs on the most frequently viewed parts of our software e.g. Top of the wikipedia article namespace. It can also be considered as a critical fix.
Functional issue If the bug in software prohibits a user from either exiting or moving forward in the system, it can be considered as a critical fix
When in doubt Ping nzr, rho, or pginer on #wikimedia-design for support
What happens if the bug isn't considered critical?
We will endeavor to fix it in a timely manner and let the fix roll out as part of the weekly deployment cycle.