"In a well-integrated dual pair of partners so adopt each other's mannerisms and style of behavior that an external observer are virtually indistinguishable." (taken from the Gulenko 2 duality description on socionics.org)

So a dualized person will appear from the outside very similar to his/her dual. I expect if you've experienced duality before, you can "dualize yourself" later without the dual around, by calling on what you learned and experienced with the dual.