^ I agree with this.
Keep in mind that HP books sold in the US were edited for US English.
Which is a shame. I would've wanted to keep them purely British.
I like seeing quirky little words or phrases I've never heard before. And it's not like a completely different language that would leave me confused. It's just a little difference.
I sometimes fight with Grammarly over spelling. I know it's not good to mix localities but some of it just looks so wrong with American rules.
I've seen complaints from Aussie writers that some readers thought their spelling was incorrect. Maybe at the very beginning just leave a note saying which spelling variant you're using. Hopefully that will shut them up.