***I don't accept the premise that the scrolls weren't changed til after Constantine. Pre-Constantine proto-orthodoxy existed. Hello.***
So, did someone sneak into all the Roman libraries and change the scrolls? What type of eraser would be used for that type ink? did they shift the rest of the words to make room for these "interpolations" or did they just try to squeeze the new words in between the lines or margins? They din't have word wrap at that time.
To understand the problem take a finely written modern book and squeeze in some new text without leaving evidence of tampering. It can't be done without completely re-writing or resetting by shifting the remainder of the type.
Again, repeating, I don't accept your premise. To assume those writings are the same today as existed in Rome is a reach. To hang your hat on the credibility of Origen is a bit shakey. You're seemingly unaware his credibility, even among Catholics, isn't exactly pure as the wind driven snow.