This highlights the differences between 2.5 and 2.4.
Read that white paper and be especially attentive to field level changes. Most times new segments are optional so can be left in the message definition in the up level message.
I have done this kind of thing multiple times. You can also go back level although that requires more analysis (some fields can get truncated for example).
email: jim.kosloskey@jim-kosloskey.com 29+ years Cloverleaf, 59 years IT - old fart.