Basically yes… but the existing legend more valuable, so there’s an eternal legend defaults and eternal legend by craft !
What i said, if you put obsidian or crystal affix to existing legend, it’ll become crystals legend !
So you can’t make eternal legend if there’s crystals affix on it or putting it obsidian
The purpose is how to make existing legend more valuable, able head to head with crystal legend and mythic item…
But if you making eternal legend by put in or combine with crystals, thats just to easy ! You could more challenging if you want eternal legend craft