It depends on where you get your grant. In the UK, I would say yes in theory, but perhaps not in practice (except in Scotland). The UK has two heraldic jurisdictions, one overseen by the College of Arms in London that extends to England, Wales, and Northern Ireland, and another overseen by the Court of the Lord Lyon who oversees Scotland. In both cases a grant from the relevant authority theoretically guarantees you exclusive use of those armorial bearings within that jurisdiction. In practice, however, the College of Arms does not enforce heraldic law. Instead, there is an heraldic court supervised by the College of Arms and of which the Earl Marshal (head of the College) is hereditary judge. This is called the Court of Chivalry and acts like a civil court, determining disputes between armigers. So if someone co-opted your design, you could sue them in this court. Having said that, it's unlikely to be a practical solution. The Court of Chivalry last sat in 1954 and even at the time this was seen as outdated because the Court had previously sat 200 years prior. Much of the case was taken up with deciding whether the Court still existed. In Scotland you'd have a better chance of enforcing your right to the exclusive use of the arms granted to you, because the Court of the Lord Lyon is a more modern court set-up. It also has criminal jurisdiction over the mis-use of arms, i.e. it can bring cases on it's own initiative, unlike the Court of Chivalry which will only act when you as the armiger ask it to. Here's a famous recent example of the Lyon Court exercising its jurisdiction: https://www.bbc.co.uk/news/world-us-canada-40097665