SFA Skin Changes

So I myself crack minecraft accounts like most people do, I get email:password form, people are selling "NFA" and "SFA" accounts and I can't tell if I have either of them, people describe SFA accounts as email:password form, and get to change the skin. Can someone explain how I can change the skin of an account that has security questions or is that considered a NFA account? If it is a NFA account, can someone help me and/or teach me how to get SFA or even unmitigated accounts. Thanks :)

Still not solved

Op hasn’t replied in 2 days. Assuming solved