Long Range (100m) USB(PC) to USB (microController USB module) Communication
If you cannot alter the PIC code, how is it going to recognise the ftdi device and program it to 115200 bd? You need to search for "transparent usb over ethernet" or extender or similar. One such device found on amazon for about $60, consists of a usb->ethernet cable box, an ethernet cable (probably not compatible with real ethernet), and an ethernet->usb hub box, which needs its own power supply.

The host sees a usb hub in front of the PIC device, and the PIC sees a usb host as usual.