ΔE 34.4, loose: different enough that you should pick on purpose. RLM 23 Red is noticeably darker, more saturated, warmer than Impish Rouge.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 34). RLM 23 Red is noticeably darker, more saturated, warmer than Impish Rouge.
The same difference applies the other way round: Impish Rouge is noticeably lighter, more muted, cooler.
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 Impish Rouge on the colour wheel See RLM 23 Red on the colour wheel
All matches: Impish Rouge equivalents · RLM 23 Red equivalents