Can I wage shameless wars of aggression against lesser powers?

[The Rock Doctor]

Absolutely!

Since we have a group of moderators, it is possible and entirely legal for one player-nation to attack another; no cooperative "scripting" of events is necessary.  The belligerents provide instructions to the moderators, who then wage the battles and report back.  The Second Pacific War is our most recent example of this, having taken place from mid-1907 through mid-1908 and ultimately involving several powers. 

On the one hand, you can aim to make some clear gains at the expense of your enemy.  On the other hand, you've got to manage diplomatic relations with the rest of the nations, lest some third party decide to kick you while you're down.  There's also the risk that in-character friction between nations will spill into out-of-character friction between the players themselves.

Of course, a cooperative, scripted conflict can also be done if both sides in the conflict are willing and able to work together on the story.  This does offer a few advantages - it tends to move faster, and there's less friction between the players, because they've already agreed upon what, if anything, they're going to lose.  On the other hand, a scripted conflict makes it more difficult for third parties to get involved, and may prevent some otherwise useful contributions from those other players.

We had a lengthy scripted conflict in the early part of this sim, between the Anahuac Empire and Rohan.  Although the specifics are now largely buried in our Archives, the events have strongly influenced play in the Americas ever since, and continue to be referenced in our stories, strategies, and play - evidence to me that the players' work was a valuable contribution to the sim as a whole.