The transparency is set on a material so to fade a figure you would need to change the transparency of every material used on each object of your figure.
So the quick answer is no.
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But if you really had to:
I've assumed you want to make a figure fade out of a scene by changing the opacity settings.
I tried to do this with a controller script, but I couldn't because the material.alpha and material.[attribute functions] that I wanted to use only appear to work in object mode, I get a script error in scene mode when I try to use them. Maybe someone else could suggest a way to modify the material.alpha from a controller script?
This leaves two options -
1) have multiple figures, e.g. 10. each with a different level of transparency. Then use visibility keys to change figures so they fade out. This involves loads of work, I wouldn't do it this way unless 2 does not work. The only reason I can think of for 2 not working is if you have multiple figures all fading in / out with the sequences overlapping.
2) Use the visibility key to make the figure disappear where you need it to fade. After rendering to video, split the clip (using a video editor) where the figure disappears and add a cross fade.
