You can move your TwistedBrush storage folder to a different or virtual drive by creating a junction (mklink) that will redirect calls to/from a directory from/to another directory: e.g. mklink /J "C:\Program Files (x86)\Pixarra\TwistedBrush\Book1" "E:\datadrive\TwistedBrushBooks\Book1". Then you have to move all your existing files on the (C) directory to the (E) drive directory. Any call from a program to the default (C) directory is redirected to the (E) directory without the program being aware of the redirection.

If you need to remove the junction, you have simply to delete it and put all the files back on the (C) directory.

You can find more information about the mklink on the Microsoft help page: https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/mklink