Yes, snoring mouthpieces are easy to fit. Stock mouthpieces are a one size fits all variety and require no fitting. However, the success rate is low.
Boil and bite snoring mouthpieces are easily fitted by heating the mouthpiece in hot water and then molding the material around the teeth while the material cools.
Custom laboratory mouthpieces are fitted by dentists or by the user and then sent to online dental laboratories.