Hi Rane,
Yes, I do it all the time
There are 6 EPROM sockets on the mainboard, where the game EPROMS (M27V322) fit in. Every (original) EPROM has a number (U86, U73, U85, U72, U84, U71), they need to be placed in the corresponding socket. There are tons of games available on the Internet. These games can be burned on an EPROM by yourself. I do this with an EPROM burner (I use a Willems EPROM Programmer GQ-4X, with the correct adapter board for M27V322 chips). Most games are 4 chips of 4MB. Some games are larger and they could need an expansion board. But it's just one or two games that need this (outback jack is one).
If you download the files, mostly they come with an extension like .U86, so you know what the chip number will be.
Sometimes they have an extension like .001. In that case:
.001 = U86
.002 = U73
.003 = U85
.004 = U72
.005 = U84
.006 = U71
Empty Chips can be found on ebay or alibaba.
After inserting a new game, you can boot up the machine. Then a lot of alarms will ring, so you need to set up the machine. This can be done in the operator menu (by turning the operator key).
For US games, an additional set-chip program needs to be run first. This uses two additional chips that need to be put on the mainboard in a riser board. OZ games don't use these (annoying) set chips.
By the way, if you want to run OZ games (the majority of them found on the Inet are), you need a "LAB Communication board". This board is placed in the most right socket under the mainboard.
So if you are going to look for an MK6 machine, make sure it has a LAB board. If not, no worries, they are not expensive.
It's not too bad to change the games, it takes about 5 minutes I guess.
Just look on the Internet for MK6 Aristocrat MAME games. You will find them easily.
Good luck, and feel free to ask questions. I've figured a lot out by myself and by this forum. I know it's quite tricky stuff, so I would be happy to help.