Hello everyone!
Thank you for Your feedback. I have just tested the mod some more. It looks like the pre-made Craft in this mod has a glitch. If I take the main stage off together With the stack seperator, the middle Connection node on the RCS stage is gone and I won't be able to Connect the main stage back on again.
I use the tweak scale mod, and it seems that some of the engines will not Connect to the Outer nodes. However they will Connect to the middle node. Even when I scale it Down it still won't Connect. This behaviour is not consistent for the RCS stage and main stage. If I manage to Connect an engine after scaling it Down, I am not able to highlight just the engine. It will only highlight the entire stage. The solution is that I highlight the engine in the staging area and right-click. Then I can scale up the engine and remove it.
Other than what I mentioned it seems to work OK.