Ehancement problem

Hi comunitty.

I need ehancing field IATA location code of LOCATIONS AND DATA/ TIMES  TAB IN NWBC I NEED PUT THIS FILED LIKE READ ONLY WHEN THE USER CLICK IN THIS TAB.

I try use class:  /BOFU/CL_FBI_GUIBB_FORM method MODIFY_FIELD_PROP but the field read only dont be changed.

Somebody know how can i do it.?

Thanks for help .