All the warnings on the jar candles say not to. I want to refill mine w/ wax and use w/ a candle warmer. I can’t think of any reason why its dangerous, but maybe its something I’m overlooking.
The warning is probably for safety purposes. When you use a jar candle, the glass heats up from the flame, and then cools when the candle is extinguished, stressing the glass somewhat each time. It is conceivable (though not very likely, I think) that reusing the jar could increase the likelihood of the jar breaking from the additional heating/cooling stress caused by multiple uses.
However, a candle warmer shouldn’t introduce that same level of stress, and it will probably work just fine.