It's hard to be constructive when something is mind-numbingly stupid Jason. As I said earlier, you can't just move an inexperienced player to fullback and expect that he'd perform at even a modestly average level. Taking bombs, cleaning up grubbers and other attacking kicks, positioning in defence, positioning the defensive line, kick returns are a few of the things that Lui would have to learn inside of what, 4 days? Steve Mortimer used to defend behind the line from memory, although not at fullback, but those days are simply long gone. We're talking near on 30 years.
To the OP. Prince may very well defend out wide, as does Soward. But there is a huge difference between defending at wing or centre and playing fullback. Every good set of six starts with a strong kick return. How often do you see either Prince or Soward returning the ball strongly from a kick? One of my problems with Moltzen playing at the back was his apathetic approach to returning the ball. We'd often give up 10 potential metres as he trotted across field either looking to pass the ball or submit in a tackle. Mitch Brown has been tremendous in this regard. And if taking bombs is so easy, why do the majority of players drop them on a regular basis?
But the most ridiculous aspect of this suggestion is that it was made 4 days from a preliminary final. Chris Lawrence - he who was directly responsible for two tries last week and several other line breaks - has spoken in recent days that the reason he was below standard last week was that the communication wasn't there last Friday. So people are honestly expecting a major re-shuffle in our defensive line before what is the biggest game of the season? You work on these things during the off-season, not 10 days out from a potential Grand Final.
As for Creagh running at Lui, that won't happen as he plays on the left and Lui defends on the left. He'll have to contend with Scott & Gasnier, not an easy prospect and I'm sure he'll be talked about at length. As I've said in other threads, front on he does a reasonable effort so I'm not worried about Scott but Gasnier will cause Lawrence and Lui trouble if they don't work together and put in greater effort than last week.