Changing multisite main site url

I have a multisite installed on domain.com. I want to change main blog url to domain.net

I have thousands blogs and i want to save these blogs still on the old domain --> usersblog.domain.com

Multi-domains of course do this for me, but how can i change ONLY the main site url?

First i thought this -> take MySQL backup -> change everything domain.com to domain.net -> manually change urls back to domain.com for users blogs from the dashboard.
BUT, this is not a good solution. Yes it works, but every image/attachement urls is not then working.

So, what is the solution change ONLY main site url?
Change only from wp_options "siteurl" and "home" and .htaccess DOMAIN_CURRENT_SITE ??