I want to repair a large hole in an interior cement wall and install an access panel. The hole right now is rough and about 12 inches wider and 4 inches taller than the 10x10 metal access panel. There are two metal-bar studs running vertically through the cement about 15 inches apart.
Should I get some wire mesh and build up the cement around the hole leaving space for the panel? If so, would I plan to attach the panel by screwing it directly to the new cement? Would the cement hold, for instance if it were 2 inches thick? How could I use the metal studs to help reinforce the cement and or the panel?

You can cut the rebar if its in your way. Drill in some Taocon screws inside the rough opening at an angle. This will act as mini rebar to help knit the old to new Crete. Just form inside that or use the access box for a form and pour. Once the Crete is set up then use tapcon screws to mount access panel