How can I change my PURL so users can access either firstname.lastname or firstname-lastname?

Allowing PURL to read multiple domain variations

You would have to update the .htaccess file.  Essentially you'll need to replace this: . *(which is just looking for the period), with [-.] *(which is looking for a period or dash).

Replace
RewriteCond %{SCRIPT_FILENAME} ([A-Za-z0-9_]+) .([A-Za-z0-9_]+)/?$ [NC] 

With
RewriteCond %{SCRIPT_FILENAME} ([A-Za-z0-9_]+) [-.]([A-Za-z0-9_]+)/?$ [NC]

And Replace
RewriteRule ^([A-Za-z0-9_-]+) .([A-Za-z0-9_-]+)/?$ http://domain.com/purlpage_campaign/index.php?name=$1http://domain.com/purlpage_campaign/index.php?name=$1$2&ID=261&page=1&ID=261&page=1 [R,L]

With
RewriteRule ^([A-Za-z0-9_-]+)[-.]([A-Za-z0-9_-]+)/?$ http://domain.com/purlpage_campaign/index.php?name=$1http://domain.com/purlpage_campaign/index.php?name=$1$2&ID=261&page=1&ID=261&page=1 [R,L]