从逻辑上来讲是不会的，先对目标施放法术，目标获得一定时间的法术效果，换上装备后，装备不受法术的影响，因为法术在施放时已经确定了目标，不包括新换上的装备。
但是实际规则就不知道了

你跟主持人提出了这个诉求，主持人肯定不会故意恶心你告诉你你用变巨术盔甲会变成超大型，如果真有这种情况，那我只能说DM不太友好

DMG p213
体型与魔法物品
“一般而言，人物找到的魔法盔甲、首饰或衣服，应该都不会有不合身的问题。因为大部分的魔法物品都很容易穿脱，有些还能自动依照穿戴者的体型而调整大小。总而言之，即使性别、种族、体型或外观特征不同，都可以穿
戴同一件魔法物品。玩家不该为了扮演一个半身人或高个子而受到惩罚。
当你以不合身作为借口时，请想好适当理由。自私贪婪的黑暗精灵所制造的斗篷就可能就只适合精灵穿着。为了不让他们精心打造的武器外流，矮人也可能打造出只有矮人能用的武器。但这些情况都是非常罕见的例外。”
原文：
When an article of magic clothing or jewelry is discovered, most of the time size shouldn’t be an issue. Many magic garments are made to be easily adjustable, or they adjust themselves magically to the wearer. As a rule, size should not keep overweight characters, characters of various genders, or characters of various kinds from using magic items. Players shouldn’t be penalized for choosing a halfling character or deciding that their character is especially tall.
Only say “It doesn’t fit” if there’s a good reason. Cloaks made specifically by the selfish, self-absorbed drow elves might fit only elves. Dwarves might make items usable only by dwarf-sized and dwarf-shaped characters to keep their items from being used against them. Such items should be the exceptions, however, not the rule.