No, you cannot get another half certificate in Old School RuneScape.
OSRS prevents players from obtaining extra Half Certificates after finishing the Shield of Arrav quest. The game locks access to these items permanently once you complete the quest.
After completing Shield of Arrav, the NPCs who give out Half Certificates stop offering them. The locations also become inaccessible. This prevents farming quest items.
You only get one chance to obtain the Half Certificate. If you complete the quest, you cannot help other players with their Shield of Arrav quest by giving them your certificate.
If you need help with other aspects of the game, you might consider looking how to get to blast furnace OSRS to improve your smithing skills. Some players also choose to buy OSRS gold to speed up their progression in the game.
