how to modify subscreen in Main screen PBO

Hi,

i have to disable one of header fields in IW22 transaction. this is Priority field in Header Tab. actually i did not find any exit where i can modify this field. there are exits available where i can modify the main screen which is 7200 of program SAPLIQS0.

but my field is on subscreen 7330.

is there any way we can modify subscreen from main screen PBO or can we do dynamic modification of any screen outside its PBO.

thanks

Rajpal