It's perfectly fine to make crosses, and then name them (Look at the lineage of the strains that are produced by other breeders. Almost none of them are created from pure, wild-collected, landrace strains, meaning that they started with genetics obtained from the work of another grower), but just selfing something that you bought and then renaming it is grimy. In that case you'd be better off calling them "Original Strain Name + S#", with "S" designating that it's the result of selfing, and "#" being the number of generations (i.e. "Dutch Passion Auto Mazar S3" = seeds produced by selfing DPAM for 3 generations in a row).
Where it gets a little bit less clear, is if you actually isolate and stabilize a specific phenotype from a strain that you obtained (i.e. you buy "Grape Ape" and only 1:4 is purple, and you self/inbreed one of those purple ones to produce a strain that's always purple). In that case, people are likely going to have a wider variety of opinions on your renaming of it.
In any case, whatever you intend to call your own, should be significantly different than whatever you originally obtained.
Where it gets a little bit less clear, is if you actually isolate and stabilize a specific phenotype from a strain that you obtained (i.e. you buy "Grape Ape" and only 1:4 is purple, and you self/inbreed one of those purple ones to produce a strain that's always purple). In that case, people are likely going to have a wider variety of opinions on your renaming of it.
In any case, whatever you intend to call your own, should be significantly different than whatever you originally obtained.