Hi Shilpi,
I have never tried it (obviously, since the program doesn't work, as you pointed out!), but I imagine that you will basically have to start again with classification.
If you have already classified Products, you would be best to make sure that they are re-transferred to the feeder system before trying to adjust the Numbering Scheme. Then afterwards, you can use the standard program to transfer the classification to GTS - that will save a lot of time.
Hope that helps.
Regards,
Dave