Most of them can change sides pretty easily, but many of them will be far more effective on one side than the other.
Loko has a brutal right hand fend, to the point where I don't think I've ever seen him carry the ball in his right. He's also got that footwork to get him on the outside (left) of his man - most players can't do that to both sides of a defender.
One player who can step off either foot is Willie Tonga, but he's played just about every game in his career at left centre, so he's bound to be better there than on the right.
And as for converting a centre to the wing, it's not that easy, especially if he's never played there much - defending kicks is such an important part of the game and requires good awareness and decision-making, which isn't going to come just because a guy is big and fast. It's generally easier to convert a fullback.
That said, if I was going to convert any of them it would be Loko.