Last we were hearing is that being able to change Normal and Specular Maps via script was not going to be possible. We have some clarification on that.
When the Materials System is first released it will not be possible to change the Normal and Specular Maps via script. The reason is that feature is just not going to be added in phase-one of the rollout. There is no other technical or mystical reason than the work to add the ability is just not being done. It is a time availability thing.
Changing the normal map requires the server to update everyone that can see the object being updated. All those that do not have the new map will have to download it. So, there is a load placed on servers and viewers for each map change. The same is currently true of texture changes, which are scriptable now. So, if people request the ability to change Normal and Specular Maps via script, it may be added at some point. Don’t bother requesting it now, unless you have a really good user case. I suspect the Lindens are waiting to see if scripting for the maps is really needed.
I am not sure we need different parameters for the maps or that scripting those changes is all that handy a thing. Since the maps follow texture’s parameters they will to some extent be programmable.
We also have been told that when we animate a texture, the Normal and Specular Maps will animate too. In general the settings for the texture (diffuse map) will apply to the Normal and Specular Maps.
We still do not know if we will be able to control the amount of displacement, depth effect, of normal maps. If we do not get that ability in the first pass, I suspect it will get added at some point.