I'm going to try attempt to convert figures wearing shorts to those wearing pants .What in your opinion would work best ? Thanks in advance ! PS my fabulous wife and I are going Christmas shopping this weekend so i get to hit the hobby shops !

Epoxy putty. There are different brands with different attributes. Some, like Tamiya, and like chewing gum in consistency, while others, like Milliputt, and more like dough (Milliputt can be sculpted easily with any tool dipped in water). Magic Sculpt if sort of in between, and also can be shaped with a wet tool.

Id really recommend Magic Sculpt. Excellent to work with, easy and has a good working time. Its a 2 part epoxy and is mixed 50/50.
Another big advantage is that it can be mixed with green stuff ... the blue and yellow 2 part expoxy favoured by warhammer fans. Green stuff is quite rubbery/elastic, but the mix of the 2 sorts, allows very fine details to be made. Especially hair and small details on the clothes.

Another recommendation I would have is Bill Chilstrom´s book ... "converting and detailing plastic figures". This is an excellent book with so many great tips, ideas and inspiration.

Thanks guys . I'll see what i can find this weekend .