Comment by yellowapple

One quick-and-dirty way to maintain the traditional model would be to copy the on-disk DB into an in-memory DB, then make any changes in memory; when the user clicks Save, the application would then move the old on-disk DB, open a new one with the old's original filename, copy everything from the in-memory DB into the new on-disk DB, and delete the old on-disk DB.

Another option would be to keep both the in-memory and on-disk copies open, and then update the on-disk version in-place with the in-memory version's data when the user clicks Save. SQLite has built-in support for connecting multiple DBs (such that you can query both in the same statement) to make this straightforward.