Actually, MICS 7.1 is available in 3 variants:
[ul]
[li]NA-MICS 7.1[/li]
[li]CDA-MICS-XC 7.1[/li]
[li]USA-MICS-XC 7.1[/li]
[/ul]
The first variant, NA-MICS, allows only one expansion cartridge to be installed on the system. The two other variants, CDA-MICS-XC and USA-MICS-XC, allow two expansion cartridges to be installed on the system.
As allworxguy and curlycord said, going from MICS 7.0 to MICS-XC 7.1 is a direct upgrade. All you need to do is power down, remove the MICS 7.0 software cartridge, insert the MICS-XC software cartridge and power up.
The only difference between CDA-MICS-XC and USA-MICS-XC is that the USA-MICS-XC has UTAM for Companion (while the CDA-MICS-XC doesn't). However, what is really important to remember is that programming will be lost if you later try to switch from CDA to USA or from USA to CDA.