I am an administrator for my SharePoint farm and am trying to apply some styles to the mysites portion of the site. However, when I try to access the mysites url directly in SharePoint Designer, i get access denied. Is there something I should be doing to get around this? This is for SharePoint 2013
Add your self as a Site Collection Administrator of the site.
If you need multiple sites: If your my sites are in a separate web application (they should be) add your account to the account policy and grant yourself full access.