two ways.
1 - copy the file "user.mlb" from the R8.1 installation to 9.0.
2 - go to "settings" - "options" - "rendering" - "browse", and redirect to R8.1 rendering library.
The better way is to copy all rendering library to the same place where you have your personal library (drive D for ex.), so you don't have worry with it and save always to the same place. with new versions just have to redirect the rendering library.
Miguel Miranda