If you simply modify the website, it is ok to have an FTP account and password; The purpose of asking your background account and password is to test the function; With the FTP account and password, you can download the source code directly from the server, whether it is provided or not.
About security
If it is an ordinary enterprise station or individual station, there will generally be no problem, because such a station does not have too high visits and has little use value, so no one will care too much.
solution
If you want to avoid maintenance personnel after modification, you need to do two things: 1. Modify the background account and password. 2. Modify the login password of FTP. The login password of FTP can be set at the place where the space is purchased. If you don't know, you can contact the person who sells your space for consultation.