Ok, all of these mods exist. Subassemleys? Subassembly loader mod! You basically described the mod. Also, use F5 to quicksave at important parts (stock game), and if you screw up, hold F9 to load that quicksave, BAM you are back there If you want to go to other planets to test stuff, use HyperEdit. Works in 0.20.2. Also, action groups can be toggled w/o electricity, so that's helpful.