"Divine Miracle (30th level): When you have expended your last remaining encounter power, you regain the use of one encounter power of your choice. In this way, you never run out of encounter powers."
I don't see you running out of Elvish Accuracy then since it says in Divine Miracle that you never run out of encounter powers. However, RAW makes the reuse of the power the DMs call due to definition of Free Action.
"Free Action: Free actions take almost no time or effort. You can take as many free actions as you want during your or another combatant’s turn. The DM can restrict the number of free actions in a turn. Examples: speaking a few sentences, dropping a held item, letting go of a grabbed enemy."
This is slightly different they using the blanket statement of " The DM can always change the rules" because as written the DM is to impose a limit that he desires on free actions right from the start. You aren't changing the text of the definition of free action. It's not a rules variant or a house rule for the DM to limit free actions, whereas if a DM decided you can use the Heal skill on yourself to give a save bonus would be the DM changing the rules as written.