Having learned some interesting behavior from experience, I'd like to share with anyone interested. I wanted to install an aftermarket remote starter on my wife's 2002 Montana. Because it uses PK3 keys, manuals stated an additional PK3 key placed inside an additional transponder module was required. I found a shortcut that works for me because I don't value the PK3 key security anyway. I simply duc-taped an original PK3 key inside the steering column, next to the ignition module. Now the very expensive PK3 keys don't work, but cheap hardware store copies do. Also the remote starter works fine without the additional transponder expense.
What I learned could save someone simply wanting extra keys money on any vehicle equipped with PK3 security keys. Just do my duc-tape trick, and buy as many cheap hardware-store key copies as you like.