Do you mean that the installation EXE for the FTDI driver removes the installed Casio Driver, just like the installation of the Casio driver removes the installed FTDA driver?
In that case, it may be possible to set the port manually, depending on the drivers. After you install the Casio driver, go into Control Panel/Device manager, open the virtual COM port and select Port Settings/Advanced. Change the COM port number to something other than the default. Then install the FTDI driver. If that doesn’t work, try it with the drivers installed in the opposite order.
