Somehow my database have two instances of the same Composer block. This probably happened because I used Page Type Builder (1.3.1) without specifying a GUID, and when deploying to a load-balanced environment where each server generated their own Composer block based on the PTB class (but with different GUIDs).

I did not discover this issue untill recently, and my problem now is that both blocks are in use by 7-15 rows in the table "tblPage". 
I tried simply changing the fkPageTypeID fields to try to make the pages use just one of the two duplicates, hoping to be able to delete the other duplicate in Admin Mode (without any "depending pages" issues). However, this did not work as expected, giving me the following error:
PageTypeBuilder.PageTypeBuilderException: The function is not of type MyComposerBlock.

I guess I'd have to delete one of the blocks from the published version of the composer pages, and somehow delete previous versions of the composer page, so that there is no dependencies in the database, before finally deleting the duplicate block in Admin Mode.

But perhaps it is possible to do this in a simpler way in the database?