You can load a 3DO cel file by choosing Acquire > 3DO CelReader from the File menu. The CelReader plug-in loads the cel into Photoshop, where you can make changes. As the CelReader reads the cels, it maintains all settings of the original cel.

Note: You should currently only open one cel at a time or the settings won't be maintained appropriately.

Note that the Pioneers folder of 3DO Toolkit 1.5 contains a plug-in that makes it possible to open a cel instead of choosing Acquire.