I just tried the script and there is one thing that could be done better. In case of converting MR Arch&Design material, if A&D material has translucency, which in MR is done as a part of refraction, refraction in CoronaMTL that is created is set up too, but translucency in Corona works different.
If it is possible, I would add some checking mechanism, and in case translucency in A&D material would be enabled, converted CoronaMTL would always have refraction level set to 0.