ΔE 24.2, loose: different enough that you should pick on purpose. Medium Magenta is noticeably lighter, more saturated, warmer than Kakophoni Purple. They are different kinds of paint: Citadel Kakophoni Purple is an opaque base/layer paint and Golden Medium Magenta is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Medium Magenta is noticeably lighter, more saturated, warmer than Kakophoni Purple. They are different kinds of paint.
The same difference applies the other way round: Kakophoni Purple is noticeably darker, more muted, cooler.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Kakophoni Purple on the colour wheel See Medium Magenta on the colour wheel
All matches: Kakophoni Purple equivalents · Medium Magenta equivalents