No THERE's a cliche phrase - change agent. Like most middle managers feel like AGENTS of change. Sure, we all instigate/catalyze changes from time to time. Some of us more than others. But most of the time, we are needing to pick up the ball - someone else's ball - and make it work.
That's the nature of management - we make things work and we execute a vision, goal, strategy or change - many of them - that comes our way from somewhere else. The best middle managers get this and embrace this. It is what we do (and yes, we need to initiate changes, too)
So I might reword change agent to be called - change baker. Like that? We put the ingredients together and bake a change. Are your changes fully baked?
In any event, check out this post from Eric Brown called, So You Want to Be a Change Agent. Good tips for both change agents and change bakers.