If you want to turn particular storey levels off in all sections/elevations, you can do this in the 'Storey Settings' dialogue.
If you want to turn of all storey markers of in a single section/elevation, you can do that in the 'Section/Elevation Settings' dialogue.
If you want to turn off one particular storey level in one particular section/elevation, I don't think you can do this (except for cover with white lines and fills).
As far as I know storey levels are not something you can control with Graphic Overrides.
Barry.
One of the forum moderators.
Versions 6.5 to 25
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10