So old topic, but I have the same question essentially and this topic turned up in search. Though I would like to change icons in multiple workflows. They're not very aesthetic icons and I would prefer to make custom icons and replace. However, I assume they're bundled in the file actions workflow, as with other respective icons and can't be replaced?
Though I I hate to compare apps Alfred is more pleasurable to use / more similar to spotlight than Launchbar, but has half the style factor.