verification code if your not the owner of the site

How can I verify a website for a client. I'm not the owner only the webdesigner. I don't think that they have verified the domain where the new wordpress website will get live on. (Now that's an old html website) In Smart Crawl you have to fill in the site verification code. But how can I get that if I'm not the owner?
And an other question...Is it possible with rebranding to change the admin dashboard for a client. So they only see menu items they really need. ?