Hi Jose,
For only 100 reports it would take you far less time to manually update the reports than write an application to do the same.
The problem is in an App you have to add a lot of error handling because the SDK will not allow you to map fields manually. It auto-maps the fields and if the SDK cannot resolve the field types it simply deletes the field which of course breaks your report. So now you have to manually "fix" the report anyways.
So I suggest rather than spending a few weeks writing an app and debugging it, it would be a lot quicker to simply update the reports in CR Designer and then use the Verify Database function and preview the reports to validate they are returning correct data.
Don't for get to update the subreport connections also....
Don