I have done earlier such a manipulation, but I was using such a strategy:
I was having 2 pages:
index.php – one pointing to a certain domain.
index2.php – pointing to an other domain.
And also apache was configured 2 listen 2 different domains.
Here as an example:
https://www.bulksms.md/
https://promotion.md/
When you access promotion, it redirect you to other site an change in the browser url of the site as bulksms.
Now i wont to point from unifun.am to unifun.com, but to keep in web browser unifun.am
But how to realize it in WP, I don’t have any ideas