Well an easy way to have a spear revert is to keep the pickup as a regular spear if you happen to be throwing it; otherwise what you could do is have your explosive spear with very low durability but just before it is destroyed it drops the original version of the spear. Getting the spear to transform in the player’s hands may be particularly difficult to accomplish but I don’t doubt it is possible for UE4. To me it just really seems to depend on how you want to approach it.