You don't need it strictly speaking. To edit textures, you need any program which can edit .dds files. I'm sure there must be some free editors on the net.

As for changing shields, you need 3dsmax. I also wish I had the great but greatly expensive program...

General Note: This sub forum are really for tutorials and questions related to the tutorial. If you have any general questions like these, ask in the general forum, people check there much more often, your questions will be answered quicker