I have a custom protocol that I'm looking at in wireshark. I thought it'd be useful if wireshark could disect it for me so that I don't have to decode the hex. Although I'm doing this in my program logs, wireshark captures the whole conversation with timing info so it'd be more useful there.
Can this be easily done?
It depends on your definition of "easily". It's definitely doable - Wireshark has great support for pluggable dissectors.
README.developer is apparently the "best manual" for dissector development. Take a look, and decide for yourself.