I kinda thought about this, but the main idea of the mod was to make your ships more specialized per planet and per science pack; however, I feel like adding a simple startup setting for the metallurgic science pack rocket cargo capacity wouldn't be that hard, and more customization is almost always better, so I might do that.
Edit : Well i did that, Metallurgic science pack now have a rocket capacity of 600 by default, and that can be changed in the settings