Change mimetype of an extension

I need to change the mimetype of a file to customize the software that opens it.

Currently the mimetype is recognized as text/html.

The file has extension .pto

So I edited /etc/mime.types and put:

application/capp				pto

at the end. Then I run:

sudo update-mime-database /usr/share/mime

yes nautilus insists it’s a text/html still

Setting unlisted application as a default - #2 by vgaetera