If you want to compare the old URL and the new one, then load at least one file of the two generations into MP3tag (best would be to load one of the old ones and all the new ones).
Select the old one in the files list.
Press Alt-T to open the extended tags dialogue.
Here you see all the tags and their contents that are in that file.
Go to the first podcast-realted one.
Press the edit-button to copy the contents.
Close the extended tags dialogue.
Now select all the new files and press Alt-T again.
Navigate to the podcast-related field for which you have copied the contents.
Press the edit button, insert the contents from the clipboard.
Click on OK to close the dialogue and save the changes.
Repeat the whole process for the next field.
iTunes will not voluntarily accept the changes - you would have to force it.
If the update is something you want to do frequently, you could either add a column for the required fields in the files list and/or add an input field in the tag panel.
In general you can think about the necessity to keep "podcasts" in the iTunes podcast section or incorporate them in the ordinary music library. For this you would have to delete the podcast-related fields. Then you are free to move the files to whichever folder you want.