You can define new SPN, FMI, CM and OC Signals in your dbc and use them in the DM1 Messages definition.
As far as FMI is concerned, this transformation is only possible in a limited way, because according to J1939-73 the SPN part of a DTC is a 19 bits long field that uses the Intel format and is distributed over 3 bytes. As a result, 16 bits are contiguous (marked blue), three further bits are separated (marked red). This distribution is done in a way that makes it impossible to automatically combine the individual parts into one single signal. You must create two FMI signals:
and combine them at measurement time using CAPL. However, if the SPN value does not exceed the 16-bit range (i.e. 65535) the 16-bit signal (FMI_2) can be used alone. This approximation is true for most (but not all) signals.