There are 2 scenarios where an installer can change the email address of the Owner:
The site is still in installation and not yet released to the customer. When the installer goes to app.saltoks.com and selects the installer account > Dashboard > Edit site. As you can see the name of the site can be changed as well as the email address.
The site is already released to the customer, but the customer has not yet created an account for the site on app.saltoks.com . This means that the site has not been 'picked up' by the customer and is therefore floating around without an Owner. When the installer goes to app.saltoks.com and selects the installer account > Dashboard > Edit installation
As you can see the name of the site can be changed as well as the email address.
If the site is already in use by the customer, and released on a certain date the Installer can no longer change the email address in the installer account. Changing the Owner is the responsibility of the customer now.