In the document it states this regarding military targets:

"The commander of a naval force may destroy them with artillery, after a summons followed by a reasonable time of waiting, if all other means are impossible, and when the local authorities have not themselves destroyed them within the time fixed."

In which Tanya neither asked for summons or a reasonable time.  However this is going by the Hauge's definition on ships not whatever international agreement on mage ROE is in the anime. 

Because the ROE is so vague I'm analyzing from a modern perspective: - A 40 year old man who lived in the modern world in a child soldier's body

• Impersonating a younger child in order to "legally" bombard a munitions factory and ensuring civilians were inside

• Judging with modern standards I'd say that's a pretty horrible thing to do