If the different body parts are using "identical" textures it is very easy to adjust them. In the assembly room you will see properties section on the right side of the screen. Directly above the list of items in the scene there is a tab for "Object" and one for "Instances". Look in the Instances tab. The shaders are listed there. If you double click on the texture there it will ask you if you want to edit the master or create a new master. If you want the changes to affect all objects that use that texture just hit edit the master. That dialogue should come up, unless at some point in the past you have clicked a button that says something like "same for all masters" or something like that. I am at work so I cant say for sure. I hope that helps Esther. Good luck.