Changing Activity ID’s via Excel

I need to change about 2000 Activity ID’s because the existing activity ID’s in my schedule are longer than 20 characters. I already have the old Activity ID’s and corresponding new Activity ID’s in excel spreadsheet so I could easily import the new Activity ID’s with minimal effort.

I do not want to have to delete all of the activities with the old IDs and create New Activities with New IDs because I will loose all of my logic.

Is there an easier way???