Simple to get most of the medals.

Invulnerable:
60 b3 04 d1 a1 68 b3 04 =>
60 b3 04 02 02 68 b3 04

You will get two hits, change the last one only. If you change the first then all the zombies will be invulnerable too, strangely when I had both of these enabled I got the "zoller" medal for 100% headshots after finishing the level.

The BOOM! medal is impossible to get - the function has the proto-code:

Code: [Select]

Game.numZombiesKilledWithBarrel = 0;
DoExplosion(10, 400);
trace("Zombiekilled with barrel: " + Game.numZombiesKilledWithBarrel);
if (Game.numZombiesKilledWithBarrel >= 5)
{
Lic.Newgrounds_UnlockMedal("BOOM!");
}
But, as you can see nothing updates Game.numZombiesKilledWithBarrel. You can probably achieve it by altering Game.numZombiesKilledWithBarrel to 6 in the first line, but this would look really suspect.