18f4550 comm clarification and advice
It looks like the UART transmit line and the SPI data out line share a pin on that part.  That happens sometimes.  Some of the newer PICs have alternate pins for some of the peripherals, or have the remappable pin feature.  The 18F4550 is a rather old part.

Trying to share the pin sounds like a lot more trouble than it's worth.  Fortunately, SPI is very easy to do in firmware if you're the master.  If this PIC needs to be a SPI slave, then you probably should use a different PIC.  Otherwise, just do the master function in firmware.  SPI is very simple, so that is easy to do.  Since it's synchronous and you own the clock, it doesn't matter if the processor occasionally goes off to a interrupt routine or something.