Technically you can't have an active ITIN and an SSN at the same time. Once you have an SSN, you are supposed to contact the IRS and have them rescind the ITIN (if they haven't done so already). As far as credit scores and files are concerned, once your ITIN has been rescinded you'll need to request that your accounts and entire credit history be transferred to the SSN. With that being said, attempting to use both simultaneously is most likely going to cause you some issues, if not now, somewhere in the not too distant future, not the least of which could be your accounts/identity being flagged for possible fraud and having to go through all the motions and aggravation to prove you are the same person.
As far as adding yourself as an AU, this will do nothing for the SSN you, as far as getting approved with an issuer is concerned, and again, if they catch on to what you are doing, you risk some sort of adverse action, including possibly being blacklisted. My advice would be to rescind your ITIN, transfer your accounts and credit history to your SSN and continue to build your credit as you have been. Better things will come your way before too long. Just my 2¢
