As I mentioned in the description, the script doesn't update instantly when you are swapping weapons in the inventory due to limitations on where it can be injected. If you are equipping the blaster after equipping the sword, exit from the inventory, wait half a second to a second and it should update to have the proper +5 attack.
Here is a video demonstration. If blasters don't return to their normal stats after this delay, that means I messed up somewhere, but since the mod and the script itself is very simple all this does every time it runs is check for a main hand weapon against the following list of base melee items types, and if it returns false it constantly attempts to remove the attack bonus effect.
if (GetBaseItemType(oItem) == BASE_ITEM_SHORT_SWORD || GetBaseItemType(oItem) == BASE_ITEM_LONG_SWORD || GetBaseItemType(oItem) == BASE_ITEM_DOUBLE_BLADED_SWORD || GetBaseItemType(oItem) == BASE_ITEM_VIBRO_BLADE || GetBaseItemType(oItem) == BASE_ITEM_VIBRO_SWORD || GetBaseItemType(oItem) == BASE_ITEM_VIBRO_DOUBLE_BLADE || GetBaseItemType(oItem) == BASE_ITEM_QUARTER_STAFF || GetBaseItemType(oItem) == BASE_ITEM_GHAFFI_STICK || GetBaseItemType(oItem) == BASE_ITEM_FIST || GetBaseItemType(oItem) == BASE_ITEM_GAMMOREAN_BATTLEAXE)