Hi Madan,
If I have understood your requirement correctly, you need the Consider Parent Assignment Approver checkbox always checked by default.
There is no option in Role Import to enable it by default for all the roles.
You need to enable the checkbox at Webdynpro level.
Webdynpro Component - GRAC_UIBB_ADD_DEF
View - V_ROLE_MAPPING
Take the help of ABAPer in your team and get the checkbox enabled.
Note: Once you enable at Webdynpro application level, it would be enabled for all the roles.
Regards,
Madhu.