'has been constantly changing' is correct and usable in written English.
It is typically used to describe something that is always in a state of flux or transition. For example: "The political landscape of the United States has been constantly changing in recent years."
To make matters even more uncertain, since 2001 Congress has been constantly changing the amount of this AMT exemption.
"From its Indian assassin origins, to 2Pac's self-empowering life branding, to various manifestations of (violent) loyalty and camaraderie in media throughout the world," the concept of 'thug' has been constantly changing with cultural contexts and time, they explain.
Detailed graphs and tables reveal how FBI staffing and enforcement priorities have been constantly changing since 1986.
But I think my ideas and feelings about my sexuality have been constantly changing since I was aware of having any sexuality.
Things have been constantly changing, constantly moving, and I just hope that, you know, over the next six years, even though I'm not going to do another degree, I hope that I can achieve as much over the next period as what I've done in this period.
The recombination rates along the genome are heterogeneous and determined by unknown factors; the rates themselves have been constantly changing during evolution.
The nation's pool of jobless workers has not been constantly changing.
Since my return, I have been constantly reminded that resistance to changing anything in Mississippi, whether the flag or the heightened black poverty, is primarily a resistance to ideas that come from outside the state from South Carolina, from Mississippi writers who have emigrated, from Washington, D.C., and, most often, from the Obama Administration.
And yet at the same time, we've been constantly reporting about how Europe is changing, how one market after another is being deregulated, whether it's telecommunications, airlines, banking, postal services.
Although there are plenty of information extraction and information retrieval tools, few of them can address the two needs that RGD has simultaneously: Ontologies are constantly changing.
I wanted to focus a lot more on not getting to an end goal where you think you're beautiful, but learning to think of your body as something that's alive, that has its own language and is constantly changing and evolving.
