I went in and edited the surname of a lodger in my grandfather's household, but it changed the surname for the whole family. I thought that it had corrected it but when I went back to the family they all had the incorrect surname.
Thanks for the answer
@Jim Challis - thank you for posting your query to FamilySearch Community. I found the following in entry in the Help Centre.
"We also need to remember that the census was not created for genealogists. They are a serendipitous genealogical result of the government’s program to account for the U.S. population. Census takers may have thought the records would never be seen again, resulting in less than accurate recording. Thus, strange or obviously incorrect information is riddled throughout the census records."
"As you look for your ancestors, remember to examine each potential record with a shrewd but realistic eye. Understanding the limitations of records such as the census will help you become a better genealogist. It will also save you a lot of headaches!"
Whilst this may not answer your query, it may help you come to terms with any inaccuracies you encounter in your research.
John L. Kennedy.
In the edit process you will (or I have seen) - the process presents the question, 'Do you want to change the surname for the entire family/remaining entries?' In that circumstance where you want to only change the surname for one entry - you would choose No (in answer to that question). If you choose Yes - then it will change the surname for all entries - as you have experienced. So to change it back you need to delete your previous edit - or if that isn't available edit it yet again back to the previous surname - excepting the one entry you do wish to change.
Unfortunately I do not have screenshots or an example to walk you through the process - but hopefully those instructions will help.
I have tried what you suggested above several times, but although I check the people I want to change it changes the entire group anyway and I have not been able to change just the lodger's surname.
This is a known problem that was reported to the engineers during the Community Review. Currently, there is not a way to change it. Hopefully, there will be a fix in the near future.
Meanwhile, I suggest you might consider waiting to make surname edits on households with multiple surnames like you came across.