.. sort of close, but no banana ... unless you do the old walnut trick ..
(a) derate is similar to unbolting the big engine .. and bolting on a little one ... the max rated (available) thrust goes down and the original engine's higher rated thrust is no longer available ... in the real world with the FMC controlling the above, one may NOT retrieve the higher rated thrust as that would invalidate all the limit thrust sums .. Vmcg relates to the limit thrust associated with the particular rating
(b) flex is a part max thrust takeoff but the limit thrust sums remain based on the rated thrust level .. ie one can push up the throttles if that is to your liking on the day ...
(c) derate and flex can be combined in which case (b) applies after (a). However, the derate thrust level should not be exceeded to avoid frights .. and Vmcg/Vmca provide big frights if the thrust goes too high .. or even if it comes up too quickly sometimes
.. but, that's OK .. you're a sailor so you must be an OK sort of bloke ..