I have found 42 subscribers to FamilySearch who have posted contributions to my tree with faulty data; several of these repeated the same errors that appear elsewhere. I would like to know how to correct errors with a single post --- aside from ensuring that the accurate data are recorded on my tree.
I'm not sure if you are talking about Family Tree or Genealogies. These are two very different sections of FamilySearch.
Family Tree is the single, universal, world-wide tree that we all work in together. If you find an error there, just correct it and document the correct information with reason statements and sources. In Family Tree every person has just one record so you only need to correct a piece of information once.
Genealogies is a static, non-editable collection of user contributed trees that can very widely in accuracy and can be completely ignored or used for nothing more than a starting point for suggestions for real research. Neither you nor the person who uploaded the tree can make any changes in it. Uploads that are new enough that they are listed under a user's trees can be deleted by the user, but that is all.
In Family Tree my great-great-grandfather is found once and has all the information users have found about him and has dozen of sources.
In Genealogies my great-great-grandfather is found 140 times with the information varying and only an occasional source.2