Excluding of records from extraction

Hi Experts

1. I am in need of code to exclude the records for a particular value of the fields AUART and VBUND

For records with the following criteria should be EXCLUDED

Sales Order Type (AUART): ZCP

Trading partner (VBUND): 1261

I know that we can write the code at start routine of the transformations but what to write in

the start routine of transformations

2. I have an extractor bringing data from ECC to info cube with alternative unit of measure

Now I need to undo these conversions in the current extractor and bring in these values from a

Custom Z table from ECC using generic extractor

And I am doubted in how to undo these conversions from the current extractor to the cube

Please help me

Thank you