Honestly I don't entirely blame you for wanting to reuse the hair, especially if it took a lot to acquire it.
Regards a good or bad sign it is neither. It is not relatively related to the spell outcome. It is like when you have a candle in a jar form such as a seven day and the jar explodes. The first couple times this happened to me with a novena candle I was able to determine the cause. You know what it was? My novena saint candles were placed on a table top relatively lower to the ground, which I had positioned right next to a baseboard heater. The jars exploded on multiple occasions, because they were overwhelmed by the heatcoming out of the radiaters.
In other words the burning and melting of the plastic was due to your own neglect. First by opting to use plastic to hold a candle, any candle, please do not do this; and second by leaving it unattended and unmatched. Left to burn without supervision.
A tealight candle often comes surrounded by an aluminum like base. Keep this base on it when you burn it. Do not remove the candle from the aluminum base unless you intend to carve the candle, or place something hopefully safe under it such as a small petition paper or sigil paper. Ventilate the space while you burn it especially if you are burning petitions, herbs, or anything else which creates more smoke.
A tealight candle when left within the metallic base, on top of the honey jar, should burn fine just as long as you watch it.
I have never had a problem burning a tealight within its aluminum casing.
Lark in hoodoo like practices a candle is often used a top a jar to add extra energy as you said. And as you said this is most certainly not the only method to do this. I often visualize energy or hold or shake a jar when working with them.
Also. A jar for a sweetening spell is not necessary even if you practice folk based magic. I recently wrote and cast a successful sweetening spell by simply dressing a tealight candle with a small bit of natural raw honey and burning it in a tealight holder meant for this type of candle. No fire. No melting, no plastic. No need as well for a jar spell that needs more upkeeping or energy.
I utilize sweetening simple candle spells quite often with much success. More so I feel than I could with a jar.
In a honey jar a taglock such as hair, nails, or saliva is not necessary . In fact as I am sure you've found, it can be incredibly difficult and time consuming to obtain these things.
For further reference and help, a name paper with the individual's name in the jar can work. Simply visualizing the individual themself can work and is the simplest taglock there is. The mental taglock. Focus on their name, or a chant to connect the jar to them can work, and can be helpful for those with trouble visualizing.
I wish you luck with your spell.
In future try to keep flammable materials away from your candles and keep a good eye on them.
Never encase the candle in plastic or use a plastic base or holder to hold it. In general candle holders are not made of plastic material. There are reasons for this. Aside from melting plastic when heated can leak other materials it is made from, including cancer related agents.
Never burn a candle by or near camphor or plastics made from camphor such as celluloid. Camphor can be incredibly flammable and unstable.
Always use a fire safe holder, plate, or surface.
A ceramic plate or holder is a great option as long as it is ceramic and fire safe.
