No one ever complained about Fabian Coulthard, who was driving for PMM all year, drove for TKR in the enduros. No one had a problem with Mark Noske stepping out of his own team to drive with Ambrose a couple of years ago. Suddenly Walky does it and all hell breaks loose.
The proposed solution to this was to force all regular drivers to stay in their own cars for the enduros - and pair each of them with a ring-in, rather than putting the two regulars together in the lead car, and raffling off the drives in the other car to whoever had the biggest wallet. This was investigated by TEGA and abandoned. Pity, it would have made the enduros even more interesting.
AFAIK there is nothing in place to prevent the cross-team swap from happening again. In the past few years GRM, PMM & FPR (at least) have sacked contracted drivers part-way through the season. Anything which would prevent the Kelly swap would also prevent this from occuring. What WILL prevent it from happening again is the public backlash which would occur should they try it again. Plus I reckon that to get Tander to sign on the dotted line to extend his contract to the end of 2008, they would have had to guarantee not to do that to him again! He would have won the Championship had he been paired with Rick and got those same results, after all!