Reconfigure Job Key Flex after go live

 We configured job key flexfield with 2 segments when first went live a few years ago. Now we need to have 4 segments for job definition and migrate all employees to the new job (with 4 segments). We know this is a risky task. We would like to find out if there is a standard /recommended way of doing this with mininal impact. (We are using Finance too.) We would also appreciate if anybody could share their experience if other companies have done this before. Thanks for the information.