Can I ask for a different expression in an art commission after approving the sketch?

The finished portrait made my favourite fictional detective look pleased with himself. I'd imagined him exhausted and suspicious. I typed, 'Could you make the smile less obvious?' then remembered I'd approved that same mouth in the sketch.

I commissioned the picture for my own wall. At the sketch stage I looked closely at the coat and background and replied, 'Looks great, go ahead.' I assumed the expression would feel different once the colours were in. I didn't tell the artist that.

She says the expression was approved and changing it now would mean more work. I believe her. I also know I'll notice the smile every time I walk past the finished picture.

Should I ask whether she'd do a paid alteration, accept the result as the consequence of my approval, or admit I haven't yet worked out how to describe the expression I wanted?