That is what closures are for:

my %actions= (
    MainPage => sub { MainPage( $Persis, $UserName ) },
    Course => sub {
        EditCourse(
            $Persist,
            def(\$g{CourseID},sub{GetNewCourse()}),
            $g{Return} )
    },
    EditCourse => 'Course',
    'Create Course' => sub {
        EditCourse( $Persist, GetNewCourse($UserName), $g{Return} )
    },
    EditEvent => sub {
        EditEvent( $Persist, $g{CourseID}, $g{Return} )
    },
    'New Venue' => sub {
        EditVenue(
            $Persist,
            GetNewVenue($Persist,$UserName),
            $g{Return} )
    },
    Venue => sub {
        EditVenue( $Persist, $g{'VenueID'}, $g{'Return'} )
    },
    EditVenue => 'Venue',
    'Delete Course' => \&DeleteCoursePage,
    'Keep Course' => sub {
        if ($g{'Return'} eq 'CourseView') {
            CourseView($Persist, $UserName);
        }
        else {
            MainPage($Persist, $UserName);
        }
    },
    # ...
);
# ...
my $action= $actions{ $g{Action} };
if(  ! $action  ) {
    MainPage( $Persist, $UserName, $UserCookie );
} else {
    $action= $actions{$action}   if  ! ref($action);
    $action->();
}
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