I would like to set custom permalinks depending on categories. More specifically, if a category is 'a' or 'b', I want to display root/x/postname, and if a category is 'c' or 'd' I want to display root/y/postname. The a, b, c & d category names should not appear; instead I want a new word - 'x' or 'y'. I also really want to avoid the word 'category' in the URL, i.e. the standard root/category/categoryname/postname format (though I think the installed SEO Ultimate plugin can fix this bit).
Here's some context: I'm running a company website for a recruitment agency, with two general types of posts - jobs and blog articles. All are currently entered as posts, then categorised depending on their audience (for articles) or type (for jobs). There are two categories for articles (employer posts & candidate posts) and two for jobs (permanent & contract) - four post categories in total.
So if in either of the job categories, I want the URL to be root/jobs/postname. If in either of the article categories, root/articles/postname.
I haven't managed to achieve this with any plugins (all I've found that could have done it are buggy/outdated/unsupported). I'm assuming it must be possible with some category structure tweaking, .htaccess or other modifications?
The other issue is (if this can be done) redirects from the existing permalinks to the new format...
Any help is appreciated - thanks!