Affects of changing Standard UOM conversion in Oracle EBS

Hi,

We are in a situation where we want to change the standard UOM conversions for primary UOm to base UOM. Currently, the UOM conversion from Primary UOM (IMPRESSION) to base UOM (EACH) is as below

1 impression = 1 X each.

However, we want to change the CONVERSION as below

1 impression =  1000 x each.

Primary UOM impression is already assigned to items. items are been purchased using Oracle purchasing standard purchase orders.

What are the affects of changing the UOM conversion on

1. closed purchase orders

2. open purchase orders.

3. Finance

4. BOM usage rate.

5. Discrete work orders.

thanks