Not sure how to override a villager when he or she is coming to the island. I used the blank villager file, went to mystery island, talked to a visitor to come to my island and edited save with the villager I want. But the furniture is still wrong. Any advice?
You should use the blank willager, then proceed to go on an island, then use the code for villager swap in this thread : https://gbatemp.net/threads/acnh-code-generator.561856/
I did that, and all went well