I mean, doable is a wide range. There are indicators that you can do some pretty amazing stuff relatively safely, probably using of something like what you're thinking. Except, that was done by the ancient God-Beings that created the Slann and elves and dwarfs, and could move planets into new stable orbits, and did so because a nice round year-length is nicer. We will not get there in this quest.
And even that has the asteriks that their big project blew up and created two portals into hell, and also a giant ball of evil magic in the sky. So, maybe not that safe afterall.
So, for the purposes of the quest, there's no safe magic. There's safeish, and you get there by either using very little, or by filtering through a god. You can get battle magic level spells safeish-ish, by stacking skill and specialization, like Mathilde does for the fog spells, but it means another step away from safeish, which itself is not safe.