Some time ago I started to build Nether portal without using Diamond Pickaxe. I was satisfied, until I noticed that I added 1 extra Obsidian block on my portal.
Will portal work If I will continue building from fifth stone, like sixth stone would never exist?
WoM Coins: 606
Yep, it will still work, you can decorate your nether portal as much as you want and it will still work, as long as the base 5x4 of obsidian is still there