Talk to the admissions office. Most likely you would need to apply all over again and I imagine they would want updated exam scores. The spot for 9th grade will get filled and there may not be an opening for 10th the following year. Even if there was an opening, it may get filled by someone else who better fills out the class profile that they want. That is assuming that being abroad for a year doesn't negatively impact exam scores and the rest of the application.

You would have to apply again because if you don't take the spot for 9th grade another kid will get it. They may not have any spots for 10th grade, unless they expand at 10th for some reason.

They will have to apply again, though the schools would not require you to take any entrance exams and maybe might forego the interview.

We have applied to a few private high schools in DC but are now looking to move abroad for the 26-27 school year. After being accepted, has any one heard of being able to "defer" enrollment until the next academic year (for us that would be 27-28). Or do they expect you to apply again?