Your ECM doesnt have a removable "chip" so a reprogram is your only option regarding making a change. Older ECMs had the memory on a "prom" which plugged into a socket.....hence the marketing of a replacement "chip" with a new program on it. Newer designs (especially OBDII stuff) uses on board memory that is not removable. There are some "modules" that attach externally to the ECU.....usually you remove the connector and plug the module in between the ECU and the harness. These dont reprogram the ECU, they only modify the signal inputs or the outputs.

For the new stuff, when the ECU is built, a program is loaded. You see a lot of activity for the LS1 stuff being reprogrammed....dont know who is competent with Ford designs. Suggest you do an internet search and/or contact some Mustang performance shops in your area.