A good smith can open it up and make it sized for the RUM's or even the 338 Lapua. Some smiths will open them for the Lapua and some wont. A really good smith can machine a ring and fuse it into the face for a standard 30-06 case also. Whether it gets bigger or smaller, it will require a sako style extractor. Otherwise you are stuck with a standard magnum. Ie: 300 winnie, 7mm Rem, 7 STW, 338 winnie ect...
It is typically better to start smaller and go bigger and not the other way around despite the fact that it can be done.