I had now a look into the builtin plugin `Save Actions`. I think the asked feature could fit into this plugin; however it seems, it would need an additional tab because it is a very different approach. I for instance do not wish any autosaving of already existing, opened files, I only want that the `untitled` files are kept after reopening Geany without being asked if I want to save them. The question is, if the plugin can bypass the dialog `The file 'untitled' is not saved.` because that would be needed.
Another thing is the naming behaviour: Changing it from `untitled` to `untitled _n_` is more a core thing, not for a plugin. What do you think about changing that via a seperate Pull Request?