It can’t really be optimized as you really need 50 different materials here. Because you are using a CustomMaterial, it will also create 50 shaders (effects), even if the code is the same.
If you wanted to optimize the number of effects created (that would not change the rendering performance, only the memory used and the compilation time), you would need to create your material as a node material instead: @Deltakosh has recently added an optimization where you can reuse the same node material effect for another node material and thus avoid the creation of a new identical effect.