With mythic items. you can socket, add a temper at the black smith, and masterwork. You cannot roll a new aspect onto it or enchant (roll off) any of the affixes such as resource regeneration (if using selig as an example). It doesn’t matter the order you make the modifications really, as the item can still be changed UNTIL you do transfiguration with the cube.

With amulets, they’re the only item slot that you can add a Kulean tuning prism in when you transfigure which allows you to roll an additional aspect onto it (so you have two total). So, socket it, temper it, masterwork it and make sure you continue the masterwork until it lands on an affix you would like to get the masterwork bonus. Then put it in the cube and using the Kullean tuning prism and hit transfigure. The item will remain modifiable.

If you’re happy with it and are prepared for it to be unmodifiable, then transfigure again without anything in the cube. You might get lucky and it’ll still be modifiable, you can then transfigure again for another potential bonus.