Cancellation of measure values

 Hi all,

   I'd like to know if there is the possibility to cancel a portion of values for a certain measure.

For example:

1) I've loaded the sales (week, store and product as base intersection) from 1st January 2012 to 18th February 2013;

2) Last 2 months (January and February 2013) are composed by 100 records. Only 10 records contain fake values

 - 9 records contain sales value to be changed;

 - 1 records contains sales value to be canceled;

3) I want to reload only last 2 months, but the files contains only the records with correct values.

I'd like to

1) cancel the values of last 2 months

2) load the latest file with the 99 correct records.