Your original install is the one your computer knows about. That matters only if you want to run games from the copied folder. Then, you have to look at which EXE you are using to start BG2, Baldur.exe or BGMain.exe. Baldur.exe, no matter whether you run it from the original install or the copy, looks at your computer's system files, finds where the original installation is and runs the game from the original folder.
BGMain.exe looks for the Baldur.ini file in the same place as itself. If you've changed the pathname in Baldur.ini, BGMain.exe will let you run a game strictly from within the copied folder. So the first thing you have to do is make certain that the shortcut on your desktop is set for BGMain.exe, rather than Baldur.exe. Then you need to look in the copy of Baldur.ini and make sure the pathnames noted in the setup instructions are set to the copied folder. OK so far?
Mods, Weidu mods at least, install in the game folder where you unpack them. So uninstall DBG from your original install, install it in the copy, then doulde-click on BGMain.exe in the copy folder. You should see the saved game you just created but should see Jasper normally in a new game. Good luck.