You Can Cancel Your Switch eShop Preorders Now
Preordering a game on the Switch eShop used to be essentially the same as buying it; you were charged for the game immediately, and could not cancel the preorder. However, that process has now changed thanks to a recent eShop update.
As detailed on the Nintendo support page, you can now cancel preordered software – assuming that it is more than seven days away from release. That's the point when preordered games are typically available to pre-load, so that's when your purchase becomes final.
It appears that this new feature only applies to new preorders; if you have preorders from before the new update, you cannot cancel them for a refund.