Is there a way to change or setup different pronouns for a person? For example: persons who go by they/them instead of he/him or she/her.
You are presumably referring to the modifiers for names available in the Sentence Template Language syntax. The answer is no. I guess it would be accurate to say that the template language was conceived more than a decade ago and the designer(s) did not anticipate the trend of gender neutrality. To RM’s credit, it did accommodate same sex couples long before some other genealogy software. If and when family tree database designers will accommodate gender neutral and transgender people accurately is an open question and a difficult one technically, I should think.