Can you add other herbs to Light Mountain henna?

I'm going to henna my hair for the first time and there seems to be an infinite amount information on adding different herbs/lemon juice to henna to do alter the effects. I just wanted to know if it is safe to do this to this particular product of should I just leave as is? For example I wanted to incorporate citric acid in the henna to bring out the color more and add cloves for better scent. Also I seen on some websites that it is best to "cure" the henna overnight before applying, I also plan on leaving the henna on overnight to make sure it sticks. So if anyone has experience with henna I would be interested in hearing your thoughts, thank you.