You could use a different design ;-) or pass the switch as last parameter and ignore it if it is undef (kind of optional parameter) or you can use a hashref as parameter and change the behaviour depending on the keys/values. But I personally dislike the last idea and would check for different design.

You could change your subroutine calls slightly to use named arguments by passing a hash rather than a list. (I'm assuming that your mixture of $ and & is a typo and that you are using named subroutines rather than code references.) Something like this code structure might fit the bill:-

...
my $yes_no = 1;
...
if ( $error_cond eq 'too long' )
{
    too_long();
}
elsif ( $error_cond eq 'no name' )
{
    no_name();
}
elsif ( $error_cond eq 'cap err' )
{
    cap_err();
}
else
{
    fallback();
}
...

sub too_long
{
    my %args = ( length => $len, type => q{Some type} );
    HTMLFTR( %args );
}
sub no_name
{
    my %args = ( request => $req, type => q{Another type} );
    HTMLFTR( %args );
}

sub cap_err
{
    my %args =  ( yes_no => $yes_no, type => q{Odd type} );
    HTMLFTR( %args );
}

sub fallback { ... }

sub HTMLFTR
{
    my %args = @_;
    ...
    if ( exists $args{ yes_no } )
    {
        print $args{ yes_no } ? "Yes\n" : "No\n";
    }
    ...
}
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By using named parameters it no longer matters what order you pass the arguments or whether some or all are present. I hope this idea is helpful.