Security package

I purchased a new 2004 Venture LT fully loaded, VCR, etc. and found out after the fact that they didn't put a security package on it which means I can't get my llights to flash when I use the remote to open the doors. My question is can this package be installed after the fact?

I would like to know were is a location of the tift deterrent relay and body control module, because when I lock my van with a remote control key the lights do not flash.The tift deterrent system and the pannick button do not work. Please, give me more information about the system and the parts in order to locate the problem.
..............yes.........

I bought a same year and have the same problem. The chevy dealer said that I had to buy a new modular for about $500 and have them install the unit.