ΔE 15.7, loose: different enough that you should pick on purpose. Permanent Violet Dark is noticeably darker than Warlock Magenta. They are different kinds of paint: Army Painter Warlock Magenta is an opaque base/layer paint and Golden Permanent Violet Dark 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 16). Permanent Violet Dark is noticeably darker than Warlock Magenta. They are different kinds of paint.
The same difference applies the other way round: Warlock Magenta is noticeably lighter.
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 Warlock Magenta on the colour wheel See Permanent Violet Dark on the colour wheel
All matches: Warlock Magenta equivalents · Permanent Violet Dark equivalents