Requests involving change of an Accounting Period that already have historical transactions not possible via Setup > Accounting > Manage Accounting Periods should be coordinated with the Professional Services Team.
Change in an Accounting Period most especially those which already have records in it would involve modifying child accounting periods and clearing of associated transactions. The impact of such modifications should all be considered first before proceeding with the change.
An example of a need for an Accounting Period Restructure would be the decision of an organization to shorten an Accounting Period in order to shift from a calendar year to a fiscal year, e.g. freeing up Q4 of a current period to be used as Q1 of a new period or modifying the Start or End date of a Fiscal Year.
Please contact your Account Manager and let them know what you exactly want to achieve before proceeding with an Accounting Period Restructure.