I mean you can anyways, just get the people who want to be involved to agree. Me and @Moon just kos each other on certain agreements such as. You don't third party (don't KOS not metagame) when in a shootout and no spawn camping, allow them to atleast get a gun
Personally I really don't mind if two orgs agree to have a "war". I suggest you make a slightly more detailed post in the rule suggestions though, so we can discuss this in one of our admin meetings and decide on something.