Updating the signature will change it across all posts, including previously-published ones. Of course, for any posts that went out via email, subscribers will still see the old signature in their email inbox.
Besides setting your blog-wide social image, for now it’s always the first image in a post that will appear. Please feel free to write in Feedback > Feature requests if you’d like to see more control over this! Maybe we can make it happen.
Shouldn’t be too hard with a little custom Javascript. Will need some time to get back to you on that.
That code should be online again!
There’s an old discussion about hosting a custom font on your own server to work around this: Font hosting? - #3 by plejer. Would something like that work?
A while ago, @dino made a script for generating an Archive page: Creating a title index page? - #2 by cjeller1592. Maybe that would help get you started? Or were you trying to create something else?
Unfortunately there isn’t. The browser’s Developer Tools would be your best bet for now. But our CSS.horse tool might help – it lets you preview your custom theme in real-time. Then you can just copy your CSS from that tool into your blog’s Custom stylesheet field on Write.as and save the changes.