this is a UUID problem...
Each file does have a "secret number", the UUID which makes (almost) each file different.
So even if you have a drawing link with "Mypart.CATPart" in folder "OLD PART" you cannot relink your drawing to the file "Mypart.CATPart" in folder "NEW PART".
The name is the same but not the UUID. If you want to do that you need to build "Mypart.CATPart" in folder "NEW PART" from "Mypart.CATPart" in folder "OLD PART". Because the new file is build from another, it does have the same UUID.
You can do that using file/new from, or you open "Mypart.CATPart" in folder "OLD PART", make some change and save as "Mypart.CATPart" in folder "NEW PART"
With that you will be able to relink your drawing with the new file, but keeping the dimension link is another story...
Eric N.
catiav5@softhome.net