ΔE 15.7, loose: different enough that you should pick on purpose. Transparent Sepia is more saturated, cooler than Agrellan Earth. They are different kinds of paint: Citadel Agrellan Earth is a technical paint or medium and Green Stuff World Transparent Sepia is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Transparent Sepia is more saturated, cooler than Agrellan Earth. They are different kinds of paint.
The same difference applies the other way round: Agrellan Earth is more muted, 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 Agrellan Earth on the colour wheel See Transparent Sepia on the colour wheel
All matches: Agrellan Earth equivalents · Transparent Sepia equivalents