Since Vegas 6 we have had support for nested Vegas projects.

What this means is that we can import a Vegas project as a VEG file and place it on the timeline and treat it as if it were any other Media. How it does this is to make a proxy file in the background and it is this file that we see and adjust. It stays as a proxy UNTIL we move on to render, when that render format is then applied to the proxy to produce the finished article.

Now, what this means for you IF you have such a version of Vegas, is that you can achieve exactly what you want to do.

I use nested veggies all the time when needed. The option provides for a much better workflow and organised complex compositing.

Of course you could still render out each and every separate veg project and import the finished render. But with nests you can right click on the nest, select "Edit" the other veg and up pops THAT veg ready for you to edit. Once finished, you can save it with the SAME name and when you return to the first veg the nested veg will have been updated with your edits. Excellent!

Grazie