Why not allow it so that at the 40th rank + someone can change their default warcry, similar to a ninjas alias.
It just makes no sense for non-religious or atheist characters to be calling to their gods. It could be so much cooler to hear a warlord shouting
"Death to enemies of the Nexus!"
or
"Lady luck, I call for your blessing!"
It might get silly, so it would have to be strict on the ones they allow, but wouldn't it be cool?
