To reduce the sLevel, this code does work, but I haven't been able to figure out the timing needed for use with a metamagic feat:
Code:
field[fChosen].chosen.field[sLevel].value -= 1
You would also need if statements and whatnot to only apply this when using a metamagic feat, but not Heighten Spell.
If you need more help, let me know.
FYI, timing for most spells to set their sLevel is First 10000, so this would have to be after that. It may have to be later for metamagic spells (possibly even Final Phase).