Redirects can get hairy sometimes – sometimes you get a nice clean canvas of directives, sometimes it’s messy and undocumented. Whatever the case, you’re dealing with an .htaccess file. One wrong move and you can crash your site
or worse yet a clients site. So before anything else make sure you have FTP access and you create a back up of their existing .htaccess file. Don’t even be tempted to do it through Yoast – even though they allow you to edit the .htaccess file right through WordPress. I’ve seen it happen and it isn’t worth it.
So you’ve got the .htaccess file – you’re going down line by line. It can look like a jungle at times – you’ll see caching stuff, some 301 redirects, some permission stuff.