Fox used to have a field programmable JITO part, and a programming board I
think.  But they might have discontinued it.  We just order the frequency
desired.  Another choice would be to use a F84 part, with a serial port to
load to the EEPROM memory a setup configuration for a programmable part.  We
use a Cypress part, requires a 22 bit serial word to program from 15Kc up to
130 MHz.  Dual also, so you can program for two different frequencies and
mux between them.