If you want to rename a field (or a object), run a form on table 2000000041:"Field" (or table 2000000001:"Object").
Change the name in that table, leave the record and check the field (or object) in the object designer. It will your new name.
It is also possible to create/delete fields with this! And also delete objects with this.
But don't try to create a table!
The shame is:I didn't find a way for the captions