Yes, it is possible to do this.
You will need to edit the HTML code generated to change the shadow settings. In the "customizeUI" area:
The first setting indicates the transparency, the second is the resolution/blurriness, and the third is the distance from the model.
If any of these are not included in the HTML file that Live 3D saved, then defaults are being used. You can add any of these lines in the appropriate place and add your custom settings.
For more information, see Chapter 4, Section 4.8 of the User Guide, Modifying the Drop Shadow. The User Guide is available in the Help menu of Live 3D CX.