How do i make a macro that can change a value?

So i am making an archer in a Pathfinder game and i was hoping, is there any way i could include a line of script or something in my attack macro to actually tick down my amount of ammo (for instance, going from 100 arrows to 99), i know how to make it look like it by going [[(@X)-1]] but how do i make it actually take one off of the total therefore making the @X attribute reduce by one without me having to do so manually

It's not possible to automate this process without the use of the API, a feature available to Pro-level subscribers.

Or players in a game created by a Pro level subscriber.

The Aaron said: Or players in a game created by a Pro level subscriber. suppose im one of these, what then?

Hazrond said: The Aaron said: Or players in a game created by a Pro level subscriber. suppose im one of these, what then? Your GM will have to install an appropriate API script before you can do it.