Depending on which way the set is facing, you may get a slight centering change [edit: or raster tilt] in a B&W set, but nothing you could notice. The orientation of the CRT will make no difference at all.
In a color set, the orientation of the CRT as well as the direction the set faces will make a difference in the purity adjustment. The CRT effect is due to the vertical component of the earth's magnetic field. In fact, color CRTs made for the southern hemisphere are different from those made for the northern hemisphere. A color CRT made for the northern hemisphere can be used in sets built for the southern hemisphere by turning it upside down (rotating 180 degrees about its axis). This can be a nuisance since it moves the high voltage connector to the other side, but it has been done in some chassis to use imported tubes. I kid you not!
http://arcadecontrols.com/files/Misc...ous/crtfaq.htm