Making a nicer product that increases user engagement is manipulating the product to match what the user likes, not manipulating the user. Changing the order and quality of ranked news articles, bending the truth, using behavioral science to promote addictive dependence,advertising products you don't actually make are all manipulating the user.

There is a big difference and yes, "manipulating the user" is sinister.

I specifically discussed putting human faces on the landing page to get more conversions and other design changes (e.g., button color, button copy). These don't change the product, only the landing page.

That's not a lie or bending the truth. It is manipulating the user.

I would suggest you stay away from describing your business practices as "manipulation", though. Almost all connotations of that word in psychology, law, and business imply deceit.

It sounds like you are decorating the showroom to boost sales... I hope it works out well for you. I was thown by the initial desciption that sure didnt sound like faces and buttons: "I'm streaming realtime events and then running statistical models on the datastream in order to manipulate user behavior."