Consequence : The dates used to calculate Muslim holidays, and the dates used to calculate Muslim tokens will be different. This is usually not too good as you might end up, on the very same day, having an [fa] token indicating the start of Ramadan, while the [id] and [iMmmm] tokens indicate it is the 2nd of Ramadan !
Otherwise, It is best to either use the Q++ Saudi Calendar if you are dealing with Saudi Arabia, or countries in the Arabian Peninsula, or countries for which you have no reliable information. On the other hand, if you have some official announcement from local religious authorities, then you should create, and use, a custom Muslim calendar that will match those dates exactly.
•Change the list of Holidays Sets : opens the aeiou-Holidays which triggered this message so you can change the list of Holidays Sets it uses.
•Change the Script Muslim Data Source : lets you change the current script's Muslim Data Source.
•Modify the current Holidays Set : if this message was caused by a specific holidays set, this lets you open the Holidays Sets Manager, and change the properties of the set which triggered this message.