Hey! It's been 9 Years since this question has been asked but i got an answer now. I needed a Makroicon for Bufffood and wanted to use the icon of Gysahl Greens. This is what i came up with:
in german:
/micon "Gizar-Blatt" gegenstand
or in english
/micon "Gysahl Greens" item

they added a category here and there so we have more possibilities now of changing to a different icon ^^

/micon "item name" item
The icon for any item in the game, including key items, can be used as long as you have at least one in your inventory or armoury chest. If you no longer possess the item the icon will remain until the macro is edited again.
If the item used can be stacked, the macro will display how many of it are in your inventory. If the item can be used and has a cooldown timer, that will also be displayed.
High quality items will need the high quality symbol appended to the end of their name, such as /micon "hard leather " item. Browsers are unable to display it properly, but copying and pasting should still work. The symbol can also be acquired by linking an item in the chat and copying it.
https://ffxiv.consolegameswiki.com/w...ro_Icons#Items