I was going to build a switch-barrel rifle, but I abandoned the idea after I did some thinking.
Also, my smith made a good point. He said, "I've never felt the need to make one for myself, the reason being is because once I get a rifle that shoots, I don't want to have to pull it apart until I have to rebarrel it..."
And that is a very sound point he made. And why I decided just to go ahead and buy cheap 700 ADL, SPS, and BDL rifles for their actions, because you can pick them up really cheap used. Might as well have a gun in each caliber you want.
Also, for what you want, .338 Lapua and .30-06 have massively different bolt face diameters. You would have to buy 2 different bolts, as well. And those aren't cheap. You might as well have 2 different rifles.
However, I see you are in Norway, and I know yall have a 6 rifle limit, but are unlimited as to how many calibers you can own. You might be better off dropping the money on a Blaser R8 or something of that nature, that is purposely designed and built as a switch-barrel rifle.
Or, if you can find it, a Thompson Center Encore rifle. You can buy barrels in just about any caliber, even wildcat calibers, online, already properly head-spaced and ready to swap on your rifle.