Rule 758.2
If the spell or ability changes for any reason such that it will no longer fall under the category of spells or abilities for which a Game Object is untargetable, the Game Object will become a legal target for that spell or ability. Example: A 1 [M] unit reads “I can’t be chosen by enemy spells or abilities with Energy cost less than my Might.” That unit is targeted by an enemy Falling Star; in reaction to the Falling Star, the unit’s controller plays Discipline targeting that unit, bringing its Might to 3 [M]. If Falling Star resolved at that point, the unit would be unaffected by it as it resolves. Falling Star’s controller plays Eclipse before Falling Star resolves, bringing the unit’s Might to -1 [M]. When Falling Star resolves now, the unit is affected by the spell and has 6 damage marked. It dies in the following cleanup.