Not entirely sure what happened here. B9 threw a serious warning when I started the game after installing this. Here's the excerpt from my .log:
[WRN 21:41:24.707] Warning on PartSubtype 5m on module ModuleB9PartSwitch (moduleID='fairingSwitch') on part benjee10.SLS.fairing: Could not find matching module
[EXC 21:41:24.707] Exception: Could not find matching module
B9PartSwitch.ModuleMatcher.FindModule (Part part) (at <a3c2951fc74e4639820ef37d2d29f386>:0)
B9PartSwitch.ModuleModifierInfo+<CreatePartModifiers>d__10.MoveNext () (at <a3c2951fc74e4639820ef37d2d29f386>:0)
B9PartSwitch.PartSubtype.Setup (B9PartSwitch.ModuleB9PartSwitch parent, System.Boolean displayWarnings) (at <a3c2951fc74e4639820ef37d2d29f386>:0)
UnityEngine.DebugLogHandler:LogException(Exception, Object)
ModuleManager.UnityLogHandle.InterceptLogHandler:LogException(Exception, Object)
UnityEngine.Debug:LogException(Exception)
B9PartSwitch.PartSubtype:Setup(ModuleB9PartSwitch, Boolean)
B9PartSwitch.ModuleB9PartSwitch:InitializeSubtypes(Boolean)
B9PartSwitch.ModuleB9PartSwitch:GetInfo()
PartLoader:CompilePartInfo(AvailablePart, Part)
<CompileParts>d__56:MoveNext()
UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)