Get MDLX and convert your mdx model to mdl. Then, open the mdl file (it will be saved in the same directory as the mdx one), which will automatically open with Notepad and scroll to the "Sequences" (it's in the very beginning of the text); find your animation, e.g. "Stand - 1" and rename it, to e.g. "Eat - 4". Exit Notepad, after saving your changes and use MDLX again to reconvert the mdl to mdx. Your model has now a new name for the animation.
Reference:
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http://www.hiveworkshop.com/forums/tools.php?id=yzpnex