What you'll need to do is rename the wads and .dat files
e.g.
sepang2001.wad --> melbourne2001.wad
S1CT02.dat --> S1CT01.dat
melbourne2001.wad --> sepand2001.wad
S1CT01.dat --> S1CT02.dat
The insert your istanbul files and rename:
interlagos2001.wad
S1CT03.dat
I highly reccomend you back up your files!!!!!!!!
(by the way, to change the track names in the menu, go to Menu Data > PC > GP2001 > GP2001_english; open in notepad and find the track names. Be very careful to only change the track names! then save your file and hopefully the correct track names will appear
)