I didn't know Kitty and Carol were particularly close... but surely that guard ought to have recognised the name as being that of Ms./Captain Marvel?...
No, she doesn't have a codename in the MCU. The only other name she's used is Lieutenant Trouble, because the first Captain Marvel film which was set...
Cover showing the whole cast... that's typical of a finale. Plus the "what is the fate of She-Hulk and Jack" line mirrors a similar one in Iron Man's...