Space Dust vs Yellow FS33531

How close are they?

ΔE 18.0, loose: different enough that you should pick on purpose. Yellow FS33531 is noticeably darker, much more saturated than Space Dust.

Can I use Yellow FS33531 instead of Space Dust?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Yellow FS33531 is noticeably darker, much more saturated than Space Dust.

Can I use Space Dust instead of Yellow FS33531?

The same difference applies the other way round: Space Dust is noticeably lighter, 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.