You can create a second account in Windows and use it to run the client the second time. Each user has its own preferences. I use this to run a second client at a low resolution, low graphics, and no sound.
(If you want to hide the second account from the login screen, see the instructions
here.)
You can run a program as another account by creating a shortcut like this:
Target: C:\Windows\System32\runas.exe /user:<name> /savecred "C:\<folder-1>\<folder-2>\...\<folder-k>\program.exe"
Start in: "C:\<folder1>\<folder-2>\...\<folder-k>"
Note: /savecred saves the users password and can be omitted if you would like to enter it each time.
Example: (Note: I use PyLotRO in place of the Turbine launcher.)
Target: C:\Windows\System32\runas.exe /user:"DDO Box" /savecred "C:\Program Files (x86)\PyLotRO\pylotro.exe"
Start in: "C:\Program Files (x86)\PyLotRO"
Note: Quotes are required around the paths. Quotes are only needed around the username if it contains a space.