choosen modifier value substracted from attribute?

Can somebody make me an API? There is an attribute called 'Andrenaline'. The player rolls a 1d6 and then decide if she wants to use some of his 'andrenaline' points as a modifier. 6>= is a success. The basics are really easy, right? /roll 1d6+?{modifier|0} But I would like if after setting the modifier, it's choosen value would have been automatically substracted from the attribute. It's not possible as a macro...

This is doable, but you should realize that the API is only available if the creator of the campaign has a Mentor-level subscription.