Let's assume you've added a new custom article element to the GN4.XSD schema, and used it (so, there is content that references it), but you need to rename it. A possible reason may be the name conflict, e.g. you've created a custom article element that differs only in character case with standard objects (a standard object is named "table" and your custom article element is named "Table" - it won't work!).
Example
So you created a custom article element "Table", but it won't show in the Frame type dialog box in Fred because of conflict with the "table" standard element. Then, you rename your custom element to "Tables" and it displays now in the Frame type dialog box in Fred, but all the references of formats and library objects may be broken; moreover, if the article element you're importing from GN3 is named "table", you will have to adjust all XML manually before importing it.
To avoid such problems, do following:
1.First of all take a copy of the DB and work on it.
2.Now try to rename back Tables to Table in the schema and re-import it.
3.The situation should go back to how it was previously, where there was table, Table and Tables should disappears.
4.If the above condition is true then you can continue.
5.Now change manually the gn_ObjectTypeTable.gn_name from Table to Tables using an SQL query.
6.Rename the element Table to Tables in the schema.
7.Re-import the schema. At this point since the element already exists it should not create any new element and the reference should now point to Tables instead of Table.