Lameth said:Can a Metamagic Rod be upgraded from lesser to normal with the cost of the lesser deducted from the cost of the normal?
Treebore said:With arms, armor and wondrous items, I would say yes. Since these particular rods are not a charged item I would also say yes. Charged items, such as wands, staves, and certain rods, no "upgrading" would be possible, unless, maybe, if it was still unused. No upgrading potions from cure light to cure moderate, either.
And yes you calaculate it by subtracting the cost of the old from the new.