Rotate
Rotate[expr_, angle_Real]rotates an expression (literally!), try
Rotate[x+y, 45Degree](*BB[*)(x+y)(*,*)(*"1:eJxTTMoPSmNkYGAoZgESHvk5Kdh43EAiKL8ksSQzP88pv6JIQtcl5LfiS3sAg3IPAA=="*)(*]BB*) See Rotate in other contexts - Rotate used for graphics primitives