This modification allows to offer deeplinks in your directory. It is a safe modification but you are better off backing up the database and the following files:
include/tables.php
/detail.php
submit.tpl
detail.tpl
You might as well test it in your test directory first. I tested it on version 3.2 and it works great.

First: we have to add additional fields in the PLD_LINK table:

1. Open include/tables.php
FIND:

'RECPR_EXPIRED' => 'L NOTNULL DEFAULT 0'

REPLACE BY:

'RECPR_EXPIRED' => 'L NOTNULL DEFAULT 0' ,
'TITLE1' => 'C(255) NULL' ,
'URL1' => 'C(255) NULL' ,
'TITLE2' => 'C(255) NULL' ,
'URL2' => 'C(255) NULL' ,
'TITLE3' => 'C(255) NULL' ,
'URL3' => 'C(255) NULL' ,
'TITLE4' => 'C(255) NULL' ,
'URL4' => 'C(255) NULL' ,
'TITLE5' => 'C(255) NULL' ,
'URL5' => 'C(255) NULL'

2. NOW rerun the install script by pointing to install/index.php, this will update the table structure.

Second: Modify the submit form:

in submit.tpl
FIND:

<tr>
   <td class="label">{l}Description{/l}:</td>

ABOVE it, ADD:

<tr>
    <td class="label">TITLE 1</td>
    <td class="field"><input type="text"
 name="TITLE1" value="{$TITLE1|escape|trim}"
 size="40" maxlength="255" class="text"/></td>
  </tr>
  <tr>
    <td class="label">URL 1</td>
    <td class="field"><input type="text"
 name="URL1" value="{$URL1|escape|trim}"
 size="40" maxlength="255" class="text"/></td>
  </tr>  
  <tr>
    <td class="label">TITLE 2</td>
    <td class="field"><input type="text"
 name="TITLE2" value="{$TITLE2|escape|trim}"
 size="40" maxlength="255" class="text"/></td>
  </tr>
  <tr>
    <td class="label">URL 2</td>
    <td class="field"><input type="text"
 name="URL2" value="{$URL2|escape|trim}"
 size="40" maxlength="255" class="text"/></td>
  </tr>  
  <tr>
    <td class="label">TITLE 3</td>
    <td class="field"><input type="text"
 name="TITLE3" value="{$TITLE3|escape|trim}"
 size="40" maxlength="255" class="text"/></td>
  </tr>
  <tr>
    <td class="label">URL 3</td>
    <td class="field"><input type="text"
 name="URL3" value="{$URL3|escape|trim}"
 size="40" maxlength="255" class="text"/></td>
  </tr>  
  <tr>
    <td class="label">TITLE 4</td>
    <td class="field"><input type="text"
 name="TITLE4" value="{$TITLE4|escape|trim}"
 size="40" maxlength="255" class="text"/></td>
  </tr>
  <tr>
    <td class="label">URL 4</td>
    <td class="field"><input type="text"
 name="URL4" value="{$URL4|escape|trim}"
 size="40" maxlength="255" class="text"/></td>
  </tr>  
  <tr>
    <td class="label">TITLE 5</td>
    <td class="field"><input type="text"
 name="TITLE5" value="{$TITLE5|escape|trim}"
 size="40" maxlength="255" class="text"/></td>
  </tr>
    <tr>
    <td class="label">URL 5</td>
    <td class="field"><input type="text"
 name="URL5" value="{$URL5|escape|trim}"
 size="40" maxlength="255" class="text"/></td>
  </tr>

Finally Show the additional links in the details page.
To do so, we have to modify detail.php and detail.tpl

1. in detail.tpl
FIND:

<tr>
<td class="label">{l}Description{/l}:</td>
<td class="smallDesc" align="left">
{$DESCRIPTION|escape|trim}</td>
</tr>

BELOW, ADD:

<tr>
<td class="label">{l}Products/Services:{/l}</td>
<td class="smallDesc" align="left">
<a href="{$URL1|escape|trim}">
{$TITLE1|escape|trim}</a>&nbsp;
<a href="{$URL2|escape|trim}">
{$TITLE2|escape|trim}</a>&nbsp;
<a href="{$URL3|escape|trim}">
{$TITLE3|escape|trim}</a>&nbsp;
<a href="{$URL4|escape|trim}">
{$TITLE4|escape|trim}</a>&nbsp;
<a href="{$URL5|escape|trim}">
{$TITLE5|escape|trim}</a>&nbsp;
</td>
</tr>

2. in detail.php
FIND:

$data['META_DESCRIPTION'] = $rdata['META_DESCRIPTION'];

BELOW it, ADD:

$data['TITLE1']    = $rdata['TITLE1']; 
$data['URL1']    = $rdata['URL1']; 
$data['TITLE2']    = $rdata['TITLE2']; 
$data['URL2']    = $rdata['URL2']; 
$data['TITLE3']    = $rdata['TITLE3']; 
$data['URL3']    = $rdata['URL3']; 
$data['TITLE4']    = $rdata['TITLE4']; 
$data['URL4']    = $rdata['URL4']; 
$data['TITLE5']    = $rdata['TITLE5']; 
$data['URL5']    = $rdata['URL5'];

 You are done, now all plans (regular and featured will have the optional 5 additional links.
To modify the number of additional links the code above should be modified accordingly (straightforward).

To allow a lower number of additional links for regular listings a simple javascript code can be added to the radio buttons of payment to hide some of the fields when “regular” is selected. Otherwise you can juste allow the same number of links for all plans.

Another additional feature could be to check if the deeplinks come from the same domain. Use your imagination.
I think this modification can be used for all versions of phpld but I only tested it on 3.2. These steps can be done everytime you upgrade the script, so you might bookmark this page or copy its content.
Feel free to improve this mod.