/etc/udev/rules.d/10-local.rules
Find the unique info for a given device using: udevadm info -a -n /dev/ttyUSB1
ACTION=="add", ATTRS{idVendor}=="dead", ATTRS{idProduct}=="beef", ATTRS{serial}=="deadbeef", SYMLINK+="ttyFoo"
Reload the udev rules: udevadm control --reload-rules && udevadm trigger