EventMap Historical Data Issue

We have developed our tables as EventMaps, but to incorporate new columns in reports EventMaps might change in future.

Issue: When we update an EventMap i.e. add/delete a field from it, all the historical data is deleted by Optimize. Is there anyway we can stop this from happening, or are their any guidelines provided by webMethods to move this data from old EventMap to the new EventMap?

Any help on this would be greatly appreciated.

Adeel Javed