QUESTION Migrating old slugs with underscores and caps

[shawn_a]

If there are only a dozen, yeah hardcode the redirects for each one to the slug.
If there are hundreds, redirect all to a processor and have it map them doing a standard gs slug clean cl()

Either way this is gonna impact your site speed if you are not using permanent redirects.
Really the only reason to do this is SEO juice, so it might be worth it.