RTC Defect Type A- to Defect type B conversion with out losing the history.

Now we have lot of “Defect” workitem in that project area which need to be converted to "Defect-B" type. Before that I exported the “Defect” work items with all necessary fields. These Defects are in different states.

I want to create “Defect-B”  (with new category – NOT same defect category) with New workflow and extra fields. When I change the “Defect” TYPE to “Defect-B”, though the “Defect” is in “Resolved” state, when it became “Defect-B”, automatically it revert back to “Initialize” state – i.e. “Analysis” (which is configured as Initialize target state).  In this condition, RTC tool automatically clears “Resolution date” details. If I map the data in exported excel and import it with latest details, it is working fine. But the “Resolution” date and “Resolved By” details are replaced with current time and my name.

To avoid the loss of data, is it possible to change the Defect TYPE through excel import??? I tried with “Mapping” xml file as well. It is not working.  Do you have any suggestion????

 NOTE:  We are going to have both "Defect" and "Defect-B" in a common template. So the future programs based on the need they can select one of the "Defect" type for their program. So don't want to RENAME the existing "defect" as "defect-B".