Study contract law. NOONE can forbid or prevent you from making an offer to contract with another. The card agreement does state that you may not assign, transfer blah blah blah ....... under that current agreement. But if you make an offer, with consideration and they accept it under full capacity (I am assuming they hire those of capable mind) and continue to perform on the new agreement you do nonetheless have a binding contract.
I find it comical that we have allowed the credit card company to change the terms and conditions as they like with really no feasible means of rejecting them. What are the options - continue to hold/ use the account (accept) or pay the account balance in full (not accpet). Your right that is fair, as you said above JUST call them, they will tell you.
Their manipulative, predatory, malicious and unethical practices have allowed this society to get so deep into debt they only have the option of accepting the terms, they can't pay off the balance.
I tell you what, if any credit card company calls CMS , I can 100% guarantee you that CMS can send them a copy of the new agreement and probably even highlight the portion explaining the terms and condition they actually did accept and perform on AND they did have the right to counter but did not.
In my case, they cash my original cheque with the offer(acceptance/ consideration), have continued to cash the cheques for the AGREED minimum payments and have changed the correspondence address from mine to CMS, (performance). All because they don't like the new terms does not mean when they act under contract law they are absolved from have their actions count as acceptance. They are not above the law or you, they have successfully made people believe through the power of marketing and habit that you don't have any rights.
A credit card company cannot take the rights that exist in this society. How can you say, the CC company has the right to ignore the law.
All law is contract and all contracts are law.