The money printed without ECB permission would legally be counterfeit. If Greece did that and got caught (and it would be immediately obvious if done in any quantity) the consequences would presumably be catastrophic.
Imagine if the rest of the eurozone declared all Y-serial euros to be invalid. Every Greek note would become worthless outside Greece - essentially a Grexit that redenominated the tens of billions of euros that Greeks have in their mattresses.
Biting the hand that feeds IT
