Unsticking a stuck screw-type in-unit water shutoff

[NormH]

I need to replace a slightly dripping Moen 1225 cartridge. I have put part, tools and process together. My problem is I'm in a condo building an prefer to avoid a full stack shutoff if possible. I have in-wall shutoffs (see photo), but they're apparently stuck. Tried WD-40 and regular width screwdriver with some torque, no luck and afraid to strip the groove. I have a wide blade screwdriver on order. If I use a socket on the hex portion, will that turn the shutoff mechanism or turn the shutoff itself and really screw things up?

 

[GReynolds929]

The hex flats are how you thread the stop into the valve body, leave that alone. The slotted s rews is what turns. Righty tighty, lefty loosy.