No, you're right - I'm the confused one - I wasn't sure if the "access"/"friend" filters were read/treated differently in the coding than the "custom" filters one creates. Does that makes sense? I guess I would get it if I understood how the code worked. :/

So, essentially, when you cross-post to Livejournal or another site, it's simply submitting the post to the other site under whatever settings you have there.