Can the flex pipe be replaced separately to an existing Cat. Conv.? on 1999 Volkswagen Jetta

I have been told that the two parts are issued new as one permanent part....I do not believe this and wish to confirm that the flex pipe can be replaced to an existing cat.conv.

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2 answers
A factory replacement or aftermarket part may require both parts or you can check with exhaust shops in your area. They might be able to cut and weld a universal flex in.
I HAVE FOUND THIS TO BE TRUE ON VW'S