It won't over-write your custom templates but you may need to revert some before things will work right... off hand the only change I know of is to the 'mark all threds read' function which you can manually fix without reverting your templates but 3.8.2 was a long time ago, I don't know for sure that's the only change. You can probably find old threads on vbulletin.com on required template reverts (if any) between all the versions.
https://www.vbulletin.com/forum/show...rk-Forums-Read