File that behaves like database? How?

Question

Hey, i want to use a file(like database) where i can store data, but i don't want to replace the old file with the new(updated) file when i make changes. I want to change only the specific part in the file, that's it. Is that possible? I mean like database, when you make changes in sql database for example, the database isn't replaced with new file(i.e. updated database file), but only the value of a specific record in the database is changed, right? If so, is that possible with some other kind of file?