Tanks not made for holding water have weaker glass. It's not neccisarily what seals the glass nor the thickness of the trim. It's the quality of the glass itself. DO NOT risk it.
I've used reptile tanks with water but no more than half way up (for river set ups), but any higher the risk of the tank breaking from the sheer weight of the water become significant. It's not worth risking coming home to broken glass and a soggy floor and all your fish flopping on the ground.
To make the tank not such a waste for resealing, you could make it into a tide pool with shallow water and animals like urchins, starfish, smaller anemones, clams even. Small coral frags, shrimps and crabs, worms, etc. Tide pools are neat, but I wouldn't do a full aquarium in it.