This won’t work if your SP exceeds the 500k tier because then you will lose SP whenever you reinject SP you had extracted.
On a related note… an idea worth considering: now that CCP has set the precedent of having dynamically created unique items with individualized attributes via Abyssal modules, perhaps skill injectors could likewise have an “Extracted by” attribute such that it could be reinjected by the person who extracted it without penalty? This “extracted by” attribute could be removed when selling to/buying from market so as to not break the market (ie. not rely on contracts).