Disfasia,
Hard to help you out without a context!
The setProperty action can be used almost anywhere!
For instance, even before you load your movie, you could set it's _visibility to false. It will load but will not be seen until you set the _visibility to true.
That can be done in a button's actionscript, but could be done most anywhere. Same goes for all the other properties of an mc.
Remember, you're not working on a .swf... You're working on a mc that holds the .swf, so you don't even have to load another movie. If you already have that movie as a mc, you can simply apply all properties to it.
In order to help you out further, you should be a little more specific and give us more of an idea of what you're trying to achieve!
;-)ldnewbie