Really useful stuff when developing using Arduino or other USB stuff that maybe have the same [vendor]:[product]. First you need to get the serial number:
# udevadm info -a -n /dev/ttyUSB1 | grep '{serial}' | head -n1
You will get something like ATTRS{serial}=="A6008isP". With this you can create new file called 99-usb-serial.rules inside /etc/udev/rules.d/. In this file you can put one line for any devices you need changing only the serial in case of same vendor and product:
SUBSYSTEM=="tty", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="A6008isP", SYMLINK+="ttyUSB.arduino"
SUBSYSTEM=="tty", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="A9234HMO", SYMLINK+="ttyUSB.other"
In this way /dev/ttyUSB.arduino and /dev/ttyUSB.other will link to some /dev/ttyUSB* that Linux will create for your device.
All the best!