If you want to 'toggle' whether or not the Name column shows extensions, try this:
Step 1. Create two new STYLES (Settings - Preferences - Listers - Styles):
Create a style with the name ExtOFF:
Click the New Style icon and enter the name - Select the Left file display (and/or Right file display) tab
Check Format - Click Edit - Click the display tab - Check view - Check Hide file extension
Create a style with the name ExtON:
Click the New Style icon and enter the name - Select the Left file display (and/or Right file display) tab
Check Format - Click Edit - Click the display tab - Check view - UNCheck Hide file extension
Step 2. Create a left/right click button to load the two new styles:
<?xml version="1.0"?>
<button backcol="none" display="label" textcol="none" type="three_button">
<label>Ext</label>
<button backcol="none" display="label" textcol="none">
<label>OFF</label>
<tip>Extensions OFF</tip>
<function type="normal">
<instruction>Prefs STYLE="ExtOFF"</instruction>
</function>
</button>
<button backcol="none" display="label" textcol="none">
<label>ON</label>
<tip>Extensions ON</tip>
<function type="normal">
<instruction>Prefs STYLE="ExtON"</instruction>
</function>
</button>
</button>
Left click the Button to hide file extensions; Right click the Button to show file extensions