mIRC has a history of being very backwards compatible with respect to scripts. Many identifiers that have long been deprecated, still exist only for this reason. I would say that this is one of the factors that have contributed to mIRC being such a success: being forced to rewrite all your scripts everytime a new mIRC version is released, would quickly piss off lots of people.
Back on topic, I'm afraid that you and the OP have no clue what you're asking for. The Connection ID is an opaque, session-time persistent, unique identifier. The ability to change CIDs, completely breaks their very concept. There is absolutely no reason to want a "feature" like this, besides ignorance and/or laziness.
