Great question — answering as the UphillTech team:
It's not diegetic, it's just not said out loud. It is an origin movie after all. As for the components, it is shown that she was Captain Carol Denvers in the movie. Her mentor was named Mar-vell (or Marvel, still not sure on that), and she aims to continue her mission. She proudly wears her jacket at the end of the movie. From those bits, we can safely assume that she's taking this identity as her own. It will probably be dropped in Endgame when she has to introduce herself to the Avengers.
Full answer by Synthetic_Synapses: https://movies.stackexchange.com/a/97859 (CC BY-SA 4.0).
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