When deleting a preset, do NOT delete the .material file, just your texture files[.png or .jpg files.]. After you have done this, are you editing the .material to meet the new preset?
Or look at >>this tutorial<< (http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=47969.0) on how to make/export a preset.
Hope this helps ^^
~ Whisper
Yes, make sure all your file extensions and texture names match the new ones c:
And no probs floof~ <3
~ Whisper