A shape is a complex entity that can be composed of various components like
custom properties, connection points and even other shapes for extra colour
and text blocks. Replacing one shape with another is not an easy task. They
are far more complex than the shapes in PowerPoint.
For some shapes that Mike eludes to, like the flowchart shapes, the original
shape includes the geometry for various shapes. The shape provides an
interface for the use to control which parts of the shapes are visible. So a
shape may appear to switch from a square, to a triangle and then to a
circle, but all three shapes are there, it is just that any given time, only
one of the shapes are visible.
John... Visio MVP
Need stencils or ideas?
http://www.mvps.org/visio/3rdparty.htm
Need VBA examples?
http://www.mvps.org/visio/VBA.htm
Common Visio Questions
http://www.mvps.org/visio/common_questions.htm