I want something very flashy to replace the green team skin, so I can notice them and shoot them out better in game please.

Download slab6 and try to modify it yourself

me

If, let's say, a green player's body is 3 blocks tall, can I make its skin look a few blocks taller?

You need vertical striped uniform.

http://i.dailymail.co.uk/i/pix/2008/09/11/article-1054674-029DE60800000578-971_468x460.jpg

Makes the player look taller.

I don't think you can do it without also modifying the blue teams skin. THey use the same models. Pure black is on the model, and switches to the respective teams color.