If you load a new image based texture then everything using that image changes. If you tweak the diffuse or ambient settings for that image you have to do it individually for every object. Here you can see I have selected the seventh image texture in the pallete. Bryce draws the red box around the active image. Click the word Load over the left hand image (I drew the red box around that one) to bring up the Open window. Navigate to the image textures, select one, and click Open. The window disappears and the left hand image changes. Do the same in the middle to add bump or transparency images.

This only changes the image. If you need to tweak scale or specularity your best bet is to assign everything to a family so they can be selected all at once. Then changing one changes all.