Pale Rider vs Lemon Yellow

How close are they?

ΔE 43.7, loose: different enough that you should pick on purpose. Lemon Yellow is noticeably darker, much more saturated than Pale Rider.

Can I use Lemon Yellow instead of Pale Rider?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 44). Lemon Yellow is noticeably darker, much more saturated than Pale Rider.

Can I use Pale Rider instead of Lemon Yellow?

The same difference applies the other way round: Pale Rider 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.