Official Holidays have an impact on budgets and allocations, so it's best to only use this for the holidays that span all locations. You can create a special Leave Type, for example "Regional Holiday," and use that on the schedule to indicate who it applies to. Keep in mind that hours on days that Leave Types are scheduled on are not automatically subtracted from the budget. Any time dedicated to Leave would have been considered as available time.
If you need to remove project assignments that overlap with these Regional Holidays, you can click on the Leave assignment In the schedule and then in the allocation menu you can choose "Remove overlapping assignments" to remove any project assignments during that time frame.