Shortcut Dimension 1 & 2 is same Global Dimension 1 & 2 which is not possible to edit same as shortcut Dim 3-8. Because Value of Shortcut Dimension 1 and 2 is saved on all standard master and ledger tables in fields "Global Dimension 1 Code" and Global Dimension 2 Code.
So, Shortcut Dimension 1 & 2 is updated using action "Change Global Dimensions" on General Ledger Setup which will execute batch to update "Global Dimension 1 Code" and "Global Dimension 2 Code" on master and ledger tables using default dimension and dimension set ID associated with record.