807.03(d)   Changing From Special Form Elements to Standard Characters, or the Reverse, May be a Material Alteration  

A special form drawing containing a design element, color, a claim to a particular style or size of lettering, or other distinctive elements cannot be amended to a standard character drawing, unless the examining attorney determines that the amendment is not material.  37 C.F.R. §2.72.

Conversely, a standard character drawing cannot be amended to a special form drawing containing a design element, color, or a claim to a distinctive style or size of lettering, unless the examining attorney determines that the amendment is not material.  37 C.F.R. §2.72.  See TMEP §§807.14–807.14(f) regarding material alteration.