It's not easy, but what you could do is create a dataset with these two events and the CRFs involved. Then you download that as odm/xml. You open the file in a tekst-editor and scroll down to where the ClinicalData for your subject begin. You take out the rest and leave only the tags odm, study and clinicaldata: as is described at http://www.trialdatasolutions.com/tds/howto/transferdatanewversion.jsp
under paragraph "preparing the import-file".
You close the tags in reverse order, so clinicaldata, study and odm. Then you change the event-oids to match the situation you would like to have and you save the file.
When you upload it, the data will switch events.
Be aware that any discrepancies are not copied and that the audit-trail will note this import action as an edit.
Hope this gives you enough hints, if not: feel free to ask.