TL;DR: Suppose a company has made a specific ethical commitment to its customers. When selling that company, is it possible for the seller to prevent the buyer from reneging on or dropping that commitment?

Details:

I got to thinking about this the other day in relation to ethical promises from companies. Suppose Company A sells a service customers pay for monthly/annually/whatever. As part of its business model, Company A promises not to do X, and writes that promise into its customer contract. It doesn't matter what X is, but let's assume

• it's legal
• it's something other companies do
• it's something some consider to be unethical
• it's something that can be clearly defined

...like selling the customers' email addresses, or sending them advertisements in the post; something like that.

Megacorp B comes along and wants to buy Company A (in its entirety, not allowing the current owners to retain a controlling interest). Is it possible to sell it in such a way, or structure the customer contracts in such a way, that Megacorp B can't change the customer contract to drop the guarantee about X once the sale is complete? (Obviously they may lose customers doing that, ones who reject the new contract, but assume Megacorp B is okay with losing those customers.)

I tend to think it's not possible, that there would be some way for Megacorp B to get around it (perhaps by setting up a new company doing an identical service, telling the customers they're winding up Company A, and offering to migrate customers to the new service), but IANAL.