There is a lot to edit to make that old window work again..
But.. if you really want to do that change..
Here are some tips..
Searching for "__S8_VENDOR_REVISION" in source gives you a hint of where the new vendor app is coded over the old..
Removing all __S8_VENDOR_REVISION will give you this error when trying to open vendor:
2021/10/24 02:26:58 GetDlgItem : nID=516 not Found.
If you can fix that it should work, dont know, did not go that far to try that out..
If you manage to find that error and fix it and it still does not work..
You can look in to a older source (v5/v6) since I believe new shop didnt start until v10.. I could be wrong tho..
Here is a link to v5/v6 source

Password: nana1206
Good luck!