RewriteCond %{HTTP_HOST} ^mycname.domain.com$ [NC]
RewriteRule ^robots.txt$ /robots-mycname.txt [NC,L]

User-agent: *
Disallow:

RewriteCond %{HTTP_HOST} ^mycname.domain.com$ [NC]
RewriteRule ^ - [F]

RewriteCond %{HTTP_HOST} ^mycname.domain.com$ [NC]
RewriteCond %{HTTP_USER_AGENT} Googlebot [NC]
RewriteRule ^ - [F]

User-agent: *
Disallow: /