According to the repair manual and the parts manual for the 7260, there are 3 pressure relief valves on the 'port block' which is the back portion of the hydrostatic drive unit once you crack the transmission case open and can get to the drive unit. Not a normal service item - dismantling the transmission is a major shop project.
How do you know you have 'pressure building up' in your hydro transmission? There aren't any test ports directly described although the plugs on the top of the port block can probably be used for this. A test rig would have to be pretty sophisticated or model-specific.
These tractors have 3 major hydraulic circuits - the hydrostatic transmission, the power steering pump/etc. and the pump that feeds the auxiliary equipment including the 3-point hitch, a loader if attached, a backhoe if attached and any other hydraulic stuff that may be installed.
A tractor with a loader installed typically has 2 pressure relief valves in the aux equip circuit. There's one integrated in the hydro distribution block on the right side of the tractor and for OEM loaders there's one either integrated with the loader control or just next to it.
Other than maybe the loader control one, these are adjusted by shimming the spring inside the valve.