You can't arm/set the veritas with the engineers code.
It's only used for testing and entering into the programming suites.
Once you have entered a recognised engineering code the "set" led winks for so many mins then if a command isn't entered it will return back to day mode.
So changing the engineering code isn't something you need to do.I suggest you get a pro in to give it the once over and show you how to use it correctly (full,part sets etc) and ask him to get you a copy of the user manual for your version.
e manno, June 2013