ΔE 15.5, loose: different enough that you should pick on purpose. Blazing Yellow is much more muted than Flash Gitz Yellow.
Can I use Blazing Yellow instead of Flash Gitz Yellow?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Blazing Yellow is much more muted than Flash Gitz Yellow.
Can I use Flash Gitz Yellow instead of Blazing Yellow?
The same difference applies the other way round: Flash Gitz Yellow 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.