Back in 2016, forum user @charliedrewitt wrote a simple utility called Assembly Fuel Utility, which simply adjusted fuel levels in all tanks while in the editor. The original thread is here: https://forum.kerbalspaceprogram.com/index.php?/topic/141062-112-assembly-fuel-utility-v110/   He is no longer around, and I've adopted this mod and enhanced it to allow individual stages to be filled or emptied while in the editor.  I've also renamed it as you can see. As of now, locked tanks are also