ΔE 10.8, fair: the same colour family, but not a straight swap. Cavalry Brown is a little darker, cooler than Rust in Peace.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Cavalry Brown is a little darker, cooler than Rust in Peace.
The same difference applies the other way round: Rust in Peace is a little lighter, warmer.
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 Rust in Peace on the colour wheel See Cavalry Brown on the colour wheel
All matches: Rust in Peace equivalents · Cavalry Brown equivalents