Yus.

-Get the enchanted ink.
-buy a blank scroll from central thanalan.
-give the blank scroll to the npc in north shroud.
-npc copies your current weapon stats to the blank scroll
-bring the copied stat scroll to central thanalan.
-remove stats by 1 point at time for free in central shroud.
-present your modified scroll to the npc in north shroud.

-You dont get a refund on alexandrite and materia you orignally used. You will have to pick up additional alexandrite and materia to add specific stats after removing undesired stats.

-You keep your current weapon as is even after making a copy of the stats to the blank scroll.

-You retain Light count even if you modify in the middle of that arc of the relic quest.

-When i did this i picked up a copy of my weapons stats when it was i110 Novus, and it let me use the copy after i upgraded it to i115 Nexus. Stats modified appropriately and proportionally upgrade automatically to make up for the i110 to i115 upgrade.