Remapping Linux serial port device names
Solution 1:
You can use udev for this. Create a file /etc/udev/rules.d/90-rename-serial-ports.rule containing
ACTION=="add" KERNEL=="ttyS2" NAME="ttyS1"
should do it (not tested). Note the difference between "==" and "=".
Solution 2:
How about a plain mv /dev/ttyS2 /dev/ttyS1? After all most devices are just a file located under /dev.
LE: You need to do the renaming every time you boot.