What should I consider before sealing a hex jar?

The practical risks are the part I’d focus on first. Glass can crack, and sharp contents can puncture it or injure someone handling it. A second bag is not a reliable fix for that, so I wouldn’t shake or casually store a jar like that. Keep any existing one away from children and pets, and check local guidance for disposing of oil and sharp waste. Don’t pour oil down a drain or onto the ground.

I’d leave out identifying details such as a full name and birth date. A symbolic stand-in or a written description of the situation can carry the meaning for you without putting someone else’s personal information in a container that could be found or lost.

If the point is symbolic, you can keep the ritual symbolic too. Words on paper or harmless objects can represent anger, boundaries, or a wish for consequences without adding blades, contaminated liquids, or anything likely to leak. People may have different beliefs about what a spell can do, but the physical hazards are worth taking seriously either way.