Excuse me while I speculate on this issue.
There could be one of two things going on here.
1. Durring test they found that useing overrides there was a way to exploit some features in the game to essentially "cheat".
or
2. They did not want to take the support calls stemmed from people modding their client.
I would hope that the first senerio is not true and the second one is. I would assume that the first senerio is not true due to the fact that even after issue #2 the ability to use overrides is still there.
As a CYA measure they decided not to condone discussions regarding client modifications on their offical forums. Which is understandable due to the fact that people that are not as technically inclined would try these modifications and in some way mess their client up and call support to have them help them fix it. In this case I would assume that a. their support staff are not trained to deal with such issues and b. they did not budget for such support senerios. All of which is very understandable. This is all based on speculation mind you and I could be way off base but thoes are my assumptions.
My recommendataion would be that if you would like to play around with clinet modifications, and talk about client modifications dont do it on the CoH public forums and dont ask for support. It might be a good idea to do your client mods on the test server as well. That way if there is some sort of client exploit that is found you can report it to the test department and hopefully get it patched in the next release.
There is my .02 cents and I hope this post does not get nuked!