CC1125: CC1125: I need to use 4gfsk moudlation format, can I use the synchronous serial mode in infinite length mode?

Part Number:CC1125

HI:

We have use the cc1125 made a transceiver with the 2gfsk as the moulation  in synchronous serial mode. Now we need to add the 4gfsk modulation format. My question is: can I use  the synchronous serial mode in infinite length mode? Since I just changed several registers refer to modulation format/BW/deviation, but it seens didn't work.