Hi there,
This is a common misconception, which rears its head in various ways. Crystal Reports was not designed to offer the ability to create user interface. Yes, there are utilities within which affect or determine user input, but they are all related to the task of producing (printing) the report. Thus Crystal cannot 'drive' the data source to which a report is linked. You will have to build that interface, usually either through a web form or a windows form, in something like Visual Studio.
If you think about it, what you are asking is that
1. When you run the Crystal Report
2. before the report imports the data
3. It opens Excel to update the values
4. Then connects to the data
5. Then builds the report
It just isn't designed for that.
Sorry!