All Remington long actions are pretty much the same action. The only differences are bolt face diameter, and if it is a RUM action, the feed rails have been slightly widened for proper feeding of the fatter RUM cases.
They would have to open the bolt face up to the larger Lapua bolt face, and probably have to widen the feed rails even more for the super-fat Lapua cases. I would imagine they probably have to use a special Lapua magazine follower, too, to allow the feeding of the super wide cases.
I know they will have to open the bolt face, but I do not know for a fact if they have to widen the feed rails more...That is just a guess, knowing the Lapua cases are fatter in diameter than the RUM cases.