I was wondering if it's at all possible to add features to the /exit like this:

/exit [-y] [password]

Okay, first off, the -y automatically bypasses the 'confirm' box if it shows up. Second, mIRC won't exit unless the password under 'lock' has been entered.

In the meantime you can use /exitd

Or you could use this:

Tools > Options > Other
(or File > Options > Other, for all the non 6.1x users)

Then click on the "Confirm" button, and change the settings in there