ΔE 27.4, loose: different enough that you should pick on purpose. Agrax Earthshade is much more muted than Rust Tone.
Can I use Agrax Earthshade instead of Rust Tone?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Agrax Earthshade is much more muted than Rust Tone.
Can I use Rust Tone instead of Agrax Earthshade?
The same difference applies the other way round: Rust Tone is much more saturated.
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.