Advice sought re Permalinks

Hello and thanks in advance of any help!

My question is one about permalinks (I suspect the question has been asked and answered before, so I apologise – but looking through a few previous “permalink” postings I found what appeared to be conflicting answers, and I need something up-to-date and definitive if possible)

Anyway; WordPress is a system I know very little about (yet!) – notwithstanding that, I’ve been asked at short notice to administer a website, one built using WordPress 3.8.3

The site currently uses the “default” permalink URL structure, i.e.

https://www.example/?p=123

… and from what I’ve read elsewhere, I’m 99% confident that via the Settings/Permalinks section of the dashboard I can simply convert those default URLs post name URLS as in:

https://www.example.com/sample-post/

… without anything breaking. Can someone please confirm that to at least 99.9 (if not 100)%?

I am hoping too, that the same “safe” change in URL will also apply to the site pages – so that

https://www.example/?page_id=123

will convert to https://www.example/?page_id=page-title (??)

Finally, there are several hundred pages with a URL in THIS type of format:

https://www.example/?product=bits-and-bobs – I am guessing that any transition from the “default” URLS to “post name” URLS will leave these ?product= URLS unaffected? I hope so, anyway….

Thank you again for any advice on this…

Oh, something else….

As the Yoast plug-in is well, plugged in, to the dashboard, will changes I make in the standard Settings / Permalinks area on the left hand side of the dashboard actually be effective, or will any changes have to be rendered via the “SEO” / “Permalinks” Tab I see at the top of the dashboard screen?

Thanks again!

Martin