Redefining an extrusion to be a "Thin Feature"

Afternoon all,

I am about a hundred or so features into a molded part.  One of my very early extrusion features was a solid block.  I want to go back and "redefine" the feature to be a thin feature instead.  Why will SW not allow me to do this?  I get the "thin feature" option on NEW extrusion creation but once I click the green check mark I cannot go back and redefine the feature to be thin.  that option to pick thin is no longer there.

Any help would be great.

Thanks

Sid

SolidworksParts And Features