Not a ton of cfm56 experience but I believe it is set up similar to a GE or Pratt as opposed to RR.
Stuck open could generate over pressure over temp bleed, 5th stage should still regulate it but there is usually a secondary valve to isolate the engine from the manifold if stuck wide open after giving a high press/temp bleed indication.
Stuck closed you would have little air at ground idle and slightly more at flight idle. Often these stuck closed discrepancies are found at top of descent as the engine transitions from cruise to flt idle (bleed air off/low etc.).
As far as engine performance stuck closed no issue, stuck open a slight decrease in thrust/efficiency unless a secondary protection S/O valve isolates the engine then no issue just less bleed air to operate packs/trim air etc..
Like I said this is general systems knowledge, someone with more time on this engine and the wing it hangs off (737/A340/Dc-8?) of may validate or negate some of the details of my post.