You could make armistice a channeling ability...then, if you gave the akkan any orders while it was using the ability, the Armistice would immediately end...
Of course, the major drawback to this is that the akkan itself could not move in order to keep armistice up, and since armistice is often used to retreat fleets to safety, you'd basically be sacrificing a lvl 6+ akkan...
Probably not the solution you are looking for as it would probably make the ability weaker...
Another possibility (maybe) is to make armistice a toggle ability...I think that toggle abilities can have a cooldown but it's been awhile since I've worked with them...if they do, then you could sort of make this work, but it'd be rather clumsy...
Armistice would have to be toggled on...upon toggling it on, it applies a buff to the akkan that removes AM (to replicate the AM cost of most abilities)...additionally, it uses the "ApplyOrRemoveBuffToSelf" to apply a "spawner" buff to itself...that buff would apply an AoE to all nearby ships with two different finish conditions: a time limit (so armistice ends by default regardless of toggling) and a check to see that the akkan still has the original "spawner" buff....
Done properly, toggling the armistice off would remove the "spawner buff" and end the armistice early...
The biggest problem here is the cooldown though....even if you can set a cooldown, you'd want two different cooldowns (no cooldown for toggling it off, but a long cooldown for toggling it on)...and then there's the issue of the AI using the ability...
All in all, I don't think changing this ability to what you want is feasible...making it possible to terminate the ability early would require immense compromises...
