[slothtrop]

Some people have more difficulty shifting, but that aside, some factors that feed into chronotype can be more impactful than others. If you moved to the other side of the world, you would surely shift your circadian rhythm and fall back to the habit of getting up at 10am or later, eventually (faster than you think). Sunlight is a powerful factor, but there is also timing of work, social cues, food, and preference. All of that informs tendency towards morning-ness or evening-ness.

The reason this is important is you can manipulate those factors to shift, the same way traveling several time zones away would automatically make you shift.