A throw back to the 1980’s where people, mainly women had their hair permed. The person who named it was a hairdresser in the 80’s and moved to web development as soon as perms became unfashionable.

Perma, meaning permanent. It's a way your URLs are structured so that there is consistency across your whole site. You can set the structure how you want it in Wordpress by going to the Permalink tab in the left hand side menu and choosing the structure you like eg, dates showing in posts, categories etc.

When perms became fashionable they were often referred to as ‘structures’’ as sometimes the hair became very tall and often times sat about one foot above the hairline.

The 5456666877&%#- does not mean anything to a search engine as the product could be anything.

There is nothing wrong with it as Google looks at your page and doesn't care what your permalink says. It's smart enough to figure it out.

It's just a minor detail. I have done everything else right so this part doesn't matter.

Yes you should as Google can’t work out that you have changed the title and the permalink structure.

No you shouldn't as you may have a link back to that article from say LinkedIn or Facebook and if you change the permalink structure and people click on it, then you will get a 404 Error page which means that page cannot be found.

Yes you should because even if the result is a 404 page (meaning that page cannot be found), Google sends traffic to pages like that because it likes to punish website owners for changing things without informing them of that change first. Google wants to bring back burning at the stake for such offences.