First you will need to create a default subobject in your constructor:
mesh = PCIP.CreateDefaultSubobject<UStaticMeshComponent>(this, TEXT("mesh"));
Then, to set the actual mesh to use (can be done from anywhere):
UStaticMesh* meshToUse = Cast<UStaticMesh>(StaticLoadObject(UStaticMesh::StaticClass(), NULL, TEXT("pathToYourAssetHere")));
if(meshToUse && mesh)
{
mesh->SetStaticMesh(meshToUse);
}
Please note that you will have to declare “mesh” as a class variable.