Interesting post! I (59 yrs., DM1 since 2004, 183 cm, 87 kg, MDI) took up triathlon sprint in 2022 and Olympic triathlon this year in Norway - water temperatures between 14 and 16°C.
I practice carbo hydrate loading (150 g muesli, 9 IU Novorapid) 30 min before swimming 750 m (Sprint) or 1.5 km...