When combining mutations you need to consider which are different mutations of the same gene (alleles) and which are different mutations of different genes. The "super pewter" is homozygous for both pastel and cinnamon which is possible because the pastel and cinnamon mutations are on separate genes. However, the rules are different when working with alleles. Because lesser/butter, mojave, phantom/mystic, Vin Russo, special, hidden, and the normal version of the same gene are an allele group no one ball python can have more than two copies of the group. So you will not be able to make a lesser mojave mystic special for example.