Convert Category ID to Category Slug

So, I’m trying to stop using category ID and replacing them with category slug as it makes things easier for using 10 multisites and not having to worry about categories having the same ID. As long as they have the same slug, everything will work fine.

Problem being, I have the navigation using ID’s but I can’t find something like the following using category slugs instead of ID’s.

Could someone assist me with this conversion? Thank you.

Code…

[code moderated - use the pastebin for any code over the forum limit of 10 lines]