Change to permalinks in Wordpress blog resulted in 500 Internal Server Error
I'm not sure if this is a Linode-side issue, or a Wordpress-side one, so I'm posting here and there in the hopes that someone can help me. Tonight I was tinkering with my blog, which I updated a couple of days ago to the latest release. I run it on Ubuntu. I'm not very experienced with working in the command line, but I usually manage with the basics such as updating the server software and doing Wordpress installs.
So today after playing with some new themes and plugins, I decided to check out Yoast's SEO tool which runs fine. One of the recommendations was to change my permalinks from the default to another format. I chose the %post_name% one as I thought it looked the tidiest.
As soon as I hit submit, I was thrown to a 500 internal server error and can now no longer access either the site or the admin interface. I have searched online for about two hours trying to figure out the problem.
I can see the htaccess file on my server using WinSCP FTP but I am denied editing or deletion access (despite being the owner of the site). I believe this may be due to some root access changes that were recommended in the command line about a year back. Essentially I use a super user account to do everything in command line and the root user was subsumed by that. I was not happy about that, but didn't know how to reverse it (and thus take full responsibility!) So anyway, I think that might be why I can't edit the htaccess file (or CHMOD it).
I checked the wp_options table in the database using MySQL as I saw mention of a possible permalinks value that I could change, but that field value is not listed.
I should point out I do have an exported backup file of the blog from a few days ago (the 10th), so if I can get back into the admin interface, I could restore that. It's just getting back in there that is the problem!
So now I turn to you, wonderful Linode community, in the hopes that you might have some suggestions on how I can get my beloved blog back.