ΔE 10.8, fair: the same colour family, but not a straight swap. Grey Violet RLM75 is a little lighter than Dark Warm Grey.
Can I use Grey Violet RLM75 instead of Dark Warm Grey?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Grey Violet RLM75 is a little lighter than Dark Warm Grey.
Can I use Dark Warm Grey instead of Grey Violet RLM75?
The same difference applies the other way round: Dark Warm Grey is a little darker.
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.