SD card cannot be mounted as /storage/sdcard0
The internal storage is present as 'storage/emulated/0'. There is no way you can "load" the internal storage as 'storage/sdcard0' or anything else. Internal storage is always present as 'storage/emulated/0', you cannot change it.

Even with rooting I think you cannot reload the internal storage as sd card. Default storage location cannot be set like that. If your phone doesn't have that option, it's a pity and I believe there are apps which allow you to do so (caution: I haven't checked any).