I think it’s more important to accept who you are. Just pretending isn’t going to change anything, maybe deep mental health therapy can change you in some ways, but just pretending is exhausting and people will be able to tell.
For example, if you feel deep inside that you want to be an athlete, well that's a part of who you are, even if you're obese. You can embrace that by working toward becoming an athlete. Start living like an athlete in ways that you can.
In corporate situations this is a lot less ambiguous, where if you want to be promoted then you have to do the work of at least 1 rank above yourself before you're officially at that level.
If you feel like you're pretending and it's exhausting, then it either means you're not being true to yourself (you're not meant to become that) or you're suffering from imposter syndrome.