The use of the preposition “to” is idiomatically acceptable in Item #1, Item #3, and Item #5: “stylist to the stars,” “I don’t know the lyrics to that song!” and “There is a certain sweetness to your voice.”
To claim to be a “stylist to the stars” is to claim bragging rights to being the stylist of choice of those stars; in contrast, to say “stylist of the stars” means just any stylist at the beck and call of those stars.
When someone says “There is a certain sweetness to your voice,” what is meant is an undefinable or indescribable sweetness in that voice; in contrast, when “There is a certain sweetness in your voice” is said instead, the speaker categorically refers to the inherent sweetness of that voice. The semantic distinction is slight but is nevertheless perceptible to the discriminating ear.
It’s idiomatically correct to say “I don’t know the lyrics to that song!” when the speaker is referring to the one-on-one correspondence between the lyrics and the musical notes for that song; in contrast, when the speaker says “I don’t know the lyrics of that song!”, the reference is only to the text of the lyrics of the song, not to the one-on-one correspondence between the lyrics and the musical notes of that song.
Sentence #2 is grammatically flawed: “Christina Aguilera sang the theme to the 1998 animation film Mulan.” A theme, which means “a melodic subject of a musical composition or movement,” isn’t sung; it’s a theme song that’s sung. When Sentence #2 is corrected for this error, it should read “Christina Aguilera sang the theme song of the 1998 animation film Mulan.” To use the preposition “to” in this case is, in my opinion, colloquial and rather iffy.
Before closing, I must also point out that the acceptable uses of “to” for certain usages that normally require “of” are not cases of “to” overuse. They are acceptable idiomatic variations meant to indicate slight differences in the intended meaning for the same phrase form.
