ΔE 15.5, loose: different enough that you should pick on purpose. Basilisk Green is noticeably lighter, more saturated than Black Templar.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Basilisk Green is noticeably lighter, more saturated than Black Templar.
The same difference applies the other way round: Black Templar is noticeably darker, more muted.
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 Black Templar on the colour wheel See Basilisk Green on the colour wheel
All matches: Black Templar equivalents · Basilisk Green equivalents