Hi Natasha,
Please find my answers to your questions:
1. In lot of customer projects, the authorization to execute the clear package is not with the end users. If this is the case in your project, then the end users need to use the input form to make the necessary changes in the data.
2. Not very clear with the problem. Please explain.
3. There is no keyword for doing it. However, you can use *REC statement to post a value of 0. This is similar to clearing.
Please note that any clear mechanism will post the negative value, as Bishwajit has explained. And you will need to optimize. However, there are certain things to remember:
1. Optimization doesn't not remove the 0 records, unless you have the zero elimination checked in your process chain.
2. Zero elimination cannot be done if you have compressed the cube in BW.
Hope this helps.