Another option is to make the external stem on the stern deeper than it needs to be so that it effectively becomes a skeg about 2 or 300 mm long but only about 5 or 10 mm deep. It is big enough to have some effect, but it doesn't actually look as if there is a skeg there.

It is a bit like eliminating or at least reducing the rocker at the stern.

Then when you discover that you didn't really need it, you can just plane it down and glass over it and no-one will ever know it used to be there.