Turn the ECU over and remove the underside cover, I will guess at if the wires from the switch go to CJ1 and CJ2 this switch will select either stock map held in the ECU or the additional map held in the daughter board EPROMs ( there is 2 EPROMs as the GTiR ECU uses a 16bit wide / word wide data stream unlike GTR's or 200SX's ).
You can either physically remove the EPROMs and read the .bin file from them using an EPROM programmer/reader, or use datascan to "rom dump" the .bin file.. any after market ECU such as Mines, Tomei, Blitz, Top fuel ( one on ebay just now ) and other use a daughter board.. some have glued the EPROMs to the board and / or under a plastic shroud.. some have rom dump disabled..
To graphically view the .bin files you can use Rom editor or Live edit final ( I like live edit --- wrote freeware by Lawrence Mooney who also wrote Nissan Rom editor I think it's called ).
In order to make "live" adjustments to maps you need emulators as previously said. the emulators that work with live edit are Romulators, again due to 16bit you need 2 as the EPROMs are 8bit items .. typically 27C256 if I remeber correctly..