I think this is the thread RichieBoy67 meant:
https://vborg.vbsupport.ru/showthread.php?t=323946
I moved to https just recently as well, using Let's Encrypt, and I did not have any issues. I didn't use any replacements vars, but I did edit my templates and changed everything which was hard coded. I used a SQL query to find them all.
Also, this link was a huge help with some of the cleanup things:
https://www.vbulletin.com/forum/arti...forum-to-https