This shouldn’t be too hard, providing your site is set up to have all the action on the top level, url-wise. (No site.com/wprdpress/ shenanigans.)
ComicPress, by default, does half the work for you. It uses a custom slug for comics to show before your title and the default for that slug is actually /comics/. If you’ve named your comic posts by their numbers, you’ll have all your elements right there.
Now go to WordPress’ Settings/Permalinks panel and change the ‘Common Setting’ to Post Name.
That was your Easy Answer. Note, however, that…
– You may want your comics to actually have titles and only for the urls to carry the numbers. That’s a little more complicated. WP has the option to show the post number in the url bar, but it won’t be your comic number because WP counts everything you add as a post and numbers it. If you’re okay with the numbers not being consecutive, simply choose ‘Custom Structure’ as your Permalink default and enter:
/%post_id%
into the field. (Do not use the Numeric option – that’ll slap an /archive/ into the url. But apart from that it’s actually the shortcode from the Numeric option.)
If you want your old comic numbers for migration consistency, though, you’ll have to cheat a little: Set up your comic post, title and all. After saving, the form shows you the url it generated – along with an option to change that url, with no consequence to the title. (Similarly, you can start by naming your comic by the number and change the title later.) There’s no automatic option for this, though. You’ll have to do it manually.
– Your site may have some extra ‘shenanigan’ levels. (Mine’s dreadfulgate.de/wordpress/eng/andthenthetitle because the web host set it up that way and it’s a multisite.) In that case, I can’t make any promises. You may be able to hide that extra fluff by doing some .htaccess magic. (Just google ‘.htaccess url Rewrite’ and see if you find anything helpful. Actually, make that ‘WordPress .htaccess url Rewrite’ because that’ll help you find your .htaccess file, too. There may be a plugin for all that, too.
