Staffing Percentage in IT0001

Hallo,

How to change the staffing Percentage in IT0001.

We have parttime employees ... ( means the position is parttime.. org needs this position only parttime ) but for these parttime employees IT0001 staffing percentage is maintained as 100%

IT0007 - Employement percentage is maintained as 100% as well

IT0008 - Capacity utilisation is maintained as 100% as well ..

we like to correct this ... I am not sure how to change the staffing Percentage in IT0001 (is it coming from OM)

what will be the impact on IT0007;IT0008 ?

Thanks

Smitra