New Post: Changing attribute of selected shapes.

In what language are you developing? It looks like C++.

What do you mean by attributes? The feature attributes or the symbology?
For symbology you can set SelectionDrawingOptions (http://www.mapwindow.org/documentation/mapwingis4.9/group__shapefile__selection.html#gaba052e641b7ad2cc260f1390aaac5100)
It is used like Shapefile.DefaultDrawingOptions (http://www.mapwindow.org/documentation/mapwingis4.9/class_shapefile.html#ab50d2c01b4848368852ea87cbcf6e5d4)

Thanks,

Paul