Allow a custom role to modify locked periods

The Override Period Restrictions permission needs to be added in the custom role. This can be found in Setup subtab under Permissions tab (Setup > Users/Roles > Manage Roles).

1. Navigate to Setup > Users/Roles > Manage Roles.
2. Edit the Custom Role.
3. Permissions Tab > Setup subtab.
4. Add the permission Override Period Restriction.
5. Click Save.

Note: This will apply only to Locked Periods and not to closed periods. Closed Periods cannot be modified but have to be re-opened.