Will a member of the tax group can change its tax period (Financial year) to join tax group?

Yes, if a juridical Resident Person meets all the conditions for forming or joining a Tax Group except for the Financial Year condition, that person can make an application to the FTA to change the start and end date of its Tax period in order to align its Financial Year tax group however subject to condition that such tax period is not extended to more than 18 months or reduced to less than 6 months.