Unfortunately, the only customization visually is an outfit which you receive once completing the game. Originally you were supposed to be able to choose between a female or male but ultimately it had to be scrapped. Maybe in the future but no guarantees. I think there's a clip of the female pirate in the very first trailer released.
I'm going to plug my other game for a second though (forgive me) just in case you'd be interested in the future...you can't choose gender but there's a ton of visual armor/clothing options. Including dresses.
You can play an old free prologue/demo here:
After The End: APOLLO (PROLOGUE)
https://elushis.itch.io/aftertheendapollo
Full game here: (Tons of armor/clothing to mess around with)
After The End: The Harvest
https://store.steampowered.com/app/386140/After_The_End_The_Harvest/
Really glad you're enjoying Mutiny Island. Thank you!