Can't change custom field label without changing the field name, too?

Custom field names have to be unique, the civicrm_custom_field table has an additional colum "label" for the name to be displayed in forms, too, though which doesn't have any uniqueness constraints.

The custom field edit form does not allow to change the label independent of the name though and so i'm getting "name already exists" error messages ...

What i actually want is to have custom fields for bank account numbers for pledges and memberships, tied to the appropriate object type (peldge/membership) and always displaying "Account No" as lable no matter what specific objects edit form i'm in. Due to the unique constraint i now have "Account No" and "Account No2" fields, and did only manage to have both showing "Account No" as field labels in forms by directly updating the label field in the civicrm_custom_filed table. But now i can't change any other properties of the "Account No 2" field anymore as this will give me the uniqueness violation error message again ...