Multimapping 1 proxy -> to -> 2 txt files: Variable Substitution omitting content inside field

Hi experts,

I need to generate 2 distinct files with 2 different names like this pattern:

file 1: cMMYYYY   ex: c012013

file 2: mMMYYYY  ex: m012013

If I create one field for each message type, the first message type for file C and the second message type for file M, and I insert inside this field a date like MMYYYY can I use this content only for Variable Substitution and not for the result of the files?

Thanks,

Antonello