ΔE 21.5, loose: different enough that you should pick on purpose. Permanent Green Light is much more saturated than Skarsnik Green.
Can I use Permanent Green Light instead of Skarsnik Green?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Permanent Green Light is much more saturated than Skarsnik Green.
Can I use Skarsnik Green instead of Permanent Green Light?
The same difference applies the other way round: Skarsnik Green is much 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.