Pre-compile commands?

Can you put these in your .nsi file?

For instance, I want to update some SVN paths prior to compiling and including the files on those paths.

Right now I'm using a .bat file to do that first and then I'm compiling my installer. I'm using the eclipse plugin and I'm a eclipse newb so there may be something there I can do as well, but I'm really interested in having it happen when I compile the nsi script if possible.

!system

Are you asking for a way to run an external command during the compilation of your script? You can use !system or !execute to do those. (The online manual is linked to those words).