Agent Assignment does not transport to another client.

[Vineet.Mehta@mbusi.daimlerchrysler.com]

I have noticed it before as well. Sometimes there are restrictions coming
from HR that do that to the agent assignment as well. I am not sure why it
would be in your specific case. However, even if the client is not open
for Changes etc, you still go the Workflow Builder and get to the Agent
Assignment and do it locally. If you go directly to task maintenance, it
might not work. This is one of the "undocumented features".
It might give you a warning, local changes etc, not allowed, but it still
accepts the change. I hope that helps.