So I found the line to comment out to prevent MechJeb from disconnecting everything, it looks like, at least my simple test rig stopped firing all decouplers: MJ pod MJ decoupler MJ 1m MJ decoupler MJ decoupler MJ decoupler stock SRB I moved the bottom decouplers all into a stage above the pod so I could be sure not to fire them. With stock MuMechLib.dll, everything still falls apart, but making a single modification prevents this, commenting out the following line: MechJebCore.cs: 1107: //p.force_activate(); This is located in the onPartFixedUpdate() function. It took me ages to find the actual documentation in the wiki on how to set up a project to build a plugin in the first place, all I was finding was the part creation SDK. After that, it only took a few minutes to find the right code to tweak. Unfortunately, now I\'m left with this, everything gets shoved into one stage of the new / detached vessel: Trying to copy the staging from all the relevant parts into the new vessel is way beyond what I\'m going to attempt right now... I imagine we\'d have to either get all the current stages and then see which parts are being detatched, put them into the same #\'d stages in the new vessel, then go in and remove empty stages and adjust all the remainder so be 0 through N. And I\'m not even sure if that\'s doable - might have to track all the parts / staging separately because it may have already separated when we see the event?