I have used old epoxy, even resin with blackened hardener, for non labor intensive uses where I didn’t care about aesthetics. I painted the flush cut top of a dead, dry stump, paint old (and new leftover) epoxy on sawhorse feet, especially the over tall sawhorses that are stored outside, the frame of movable steps made from old stair risers that likewise live outside, the inside of an ancient pinhole rusted wheelbarrow, etc.
I’m too cheap to throw out epoxy, and it’s probably better to use it up than have it end up in a landfill.