Haven't tried this, but what about copying the duplicate chart and then importing it into the active chart?
It is possible to change the date on an encounter and save it.
You would open up the visit in the duplicate chart, copy and paste into the corrrect chart as an addendum, it would have the correct date but not be labelled as an encounter. But, the addendeum could be labelled as an enounter in the header.
Not perfect and not quick.