After many frustrating hours spent trying to make the trueSpace
mirror tool do something useful, we came up with coolmirror. It works at the vertex level
to truly flip your polyhedra. Select the axes you wish to mirror on and do it.
faq: I get a real weird display in solid shaded mode. Can this be fixed?
Probably not. 3DR in particular freaks out when it finds an object
that has had its vertices messed with, but just try rendering the object - it looks fine.