Regarding the immediate issue, my first thought would be that you made your copies in the same directory as the originals. When perl sees use ABC::HandleData, it scans through the directories in @INC and, in each one, looks for ABC/HandleData.pm. If you want to use packages in the ABC2 namespace, they need to go into an ABC2 subdirectory, not the existing ABC subdirectory.

And, since you phrased this as an OOP question rather than only as one about package management... Might it be more appropriate to subclass the existing ABC packages? Although there are (a very few) exceptions, "copy-paste inheritance" is generally inferior to the real thing.