You will not lose features, but you will lose the programming. The firmware is highly dependent on the version of RPM you have. If you are using RPM 10B, then I'd personally avoid using anything other than R02A. We are forced to use certain firmware versions due to us having to use RPM 14 for the XG100 and RPM 2 for the XL200.
In RPM, if I put in a UHF amateur frequency (440-450) and set it to wide-band, it lets me program the radio, but then the display shows "INVALID CHANNEL." If I put in a wide-band VHF (144-148), it works fine. This is the same for the XL200 and the XG100 radios that we have. I asked Harris if they could send me the feature code to enable wide-band, but have not heard back yet. We have thousands of the XG100 and I just don't like them at all. The XL200 looks promising, but there are still some short-comings in my opinion.