In order to update holidays within a Holiday timeframe, include the parameter update_only and provide within the array timeframe-holiday-array the new values for the holidays you intend to update, including in each holiday object the associated timeframe-id for that holiday. If any holidays are missing the timeframe-id parameter, it may result in undesired behavior.
The value for update-only must be set to yes for this operation to succeed as desired. If any other value is supplied or the parameter update-only is omitted, it will result in the behavior described in "Replace All Holidays in Holiday Timeframe" - see examples for more information.
IMPORTANT:
Updates to holidays are limited to workweek, observance configurations, time-of-day configurations, and recurrence. To add a different holiday, remove the existing holiday and then create the desired holiday.