Permissions on Target Version

[Rotem]

I have a newbie question:

I have added the new field Target Version, this works good.
However, I want to have only the Project Managers (or anyone define as a manager) to be able to change the value of this field.
I assume I need to change bug_update_advanced_page.php (which we are using) and have the line:
“if ( access_has_bug_level( config_get( 'roadmap_view_threshold' ), $f_bug_id ) ) {”
Changed into something that will pick up only the project managers, however not sure how to change.
Please advice,
Thank you.
Rotem.