Dressing candles with herbs and other flammable material can definitely be dangerous! When dealing with candles and fire, I don’t think there’s a 100% safe method, just a less dangerous method.
I have a video on dressing candles on my YouTube channel if you wanna check it out.
→ Dressing Candles 🕯️ Candle Magick Tips and Tricks || Witchcraft 101 [CC] - YouTube
I think that as long as you don’t use too much, you keep it away from the wick, and you have a safe method of extinguishing the flame, you’ll be okay! And when I say safe for candles, I mean smothering or snuffing. Never water!