[T2DMan]

How do you have several sites coming into your site, and have one with different robots.txt file

mail .htaccess file includes:

[PHP]RewriteCond %{HTTP_HOST} domainb.com
RewriteRule robots.txt robotsfff.txt [L]

[/PHP]

Then the robotsfff.txt file containing say a total exclusion:

[PHP]User-agent: *
Disallow: /[/PHP]

this means that the domainb.com/robots.txt shows as
[PHP]User-agent: *
Disallow: /[/PHP]

And no need to redirect the access for the robotsfff.txt file. You could do a 301 redirect back to the robots.txt file, not worth the effort.