Whether or not requalification of a WPS is required, is determined by the classification of the variable (essential/non-essential, or when applicable, supplemental essential).
Sometimes though, details in the WPS, which may be non-essential, should be thoroughly considered before revision. Just because you may techinically change a variable, doesn't mean you should.
One example is this: Sometimes we limit the filler metal diameter because of the talent it takes to jump to larger sizes. We generally don't use 5/32" diameter E7018 on pipe (so the WPS may not lis it as an option). Some projects are staffed with our better welders who can handle that size. In those cases, we may issue a revision allowing the use of the larger filler metal. We would put the burden on the supervisor to make sure the welder can handle the electrode.
Charles