what about those new MF and LF band?

The PA in all our products have a minimum TX frequency of 1.8 MHz, so they cannot be unlocked for frequencies below that minimum.

For the FLEX-3000 you will need to use a transverter to operate below 160m.  Receive has always been available, but you may need a band specific preselector (bandpass filter)  to remove the IM mixing that occurs with the AM broadcast band.

These issues are not relevant to the FLEX-6000 models since they have the capability to use the Transverter Port to output transmit signals at about a 0 dBm level on any frequency the radio will operate upon. So, at 137 and 475 kHz, you will need to supply an external power amplifier and that would take in 0 dBm levels and boost them to whatever power levels you would use to operate in those bands. 

So that your expectations are set properly, this modification is not a modification FlexRadio will do since the FLEX-3000 is a discontinued product and we are no longer updating the firmware and software for it.

If you want to save some money, you can build your own 630m teansverter.  There are several sources on the Internet for kits and plans: 
https://www.google.com/#q=630m+transverter+kit