Are you able to adjust its picture settings when it's in store mode?

No. Brightness and contrast are maxed out but it's not bad with a cheaper model.

My opinion --- in some cases, the difference between expensive and cheap boils down to the picture controls being intentionally limited for marketing effect.

So the cheap model maxed out looks like the more expensive model at medium. People can recognize the difference in the store so they opt for the more expensive one. But the actual displays themselves are virtually identical.

It may actually be cheaper to make one grade of display and differentiate using the controls.