It's the same as the detail view.
The function's name should be modified is 'get_schedule_edit_html'.
near line 915 of piCal.php
$ret = "
<h2>"._PICAL_MB_TITLE_EVENTINFO." <small>-"._PICAL_MB_SUBTITLE_EVENTEDIT."-</small></h2>
<form action='$PHP_SELF' method='post' name='MainForm'>
<input type='hidden' name='caldate' value='$this->caldate'>
<input type='hidden' name='event_id' value='$event_id'>
<input type='hidden' name='last_smode' value='$smode'>
<input type='hidden' name='last_caldate' value='$this->caldate'>
<input type='hidden' name='poster_tz' value='$poster_tz'>
<table border='0' cellpadding='0' cellspacing='2'>
<tr>
<td class='head'>"._PICAL_TH_SUMMARY."</td>
<td class='even'><input type='text' name='summary' size='60' maxlength='250' value='$summary'></td>
</tr>
<tr>
<td class='head'>"._PICAL_TH_STARTDATETIME."</td>
<td class='even'>
$textbox_start_date
{$select_start_hour}"._PICAL_MB_HOUR_SUF." {$select_start_min}"._PICAL_MB_MINUTE_SUF." <select name='event_tz'>$tz_options</select>
</td>
</tr>
<tr>
<td class='head'>"._PICAL_TH_ENDDATETIME."</td>
<td class='even'>
$textbox_end_date
{$select_end_hour}"._PICAL_MB_HOUR_SUF." {$select_end_min}"._PICAL_MB_MINUTE_SUF."
</td>
</tr>
<tr>
<td class='head'>"._PICAL_TH_ALLDAYOPTIONS."</td>
<td class='even'>
<fieldset>
<legend class='blockTitle'><input type='checkbox' name='allday' value='1' $allday_checkbox onClick='document.MainForm.event_tz.disabled=document.MainForm.StartHour.disabled=document.MainForm.StartMin.disabled=document.MainForm.EndHour.disabled=document.MainForm.EndMin.disabled=this.checked'>"._PICAL_MB_ALLDAY_EVENT."</legend>
<input type='checkbox' name='allday_bits[]' value='1' {$allday_bit1}>"._PICAL_MB_LONG_EVENT." <input type='checkbox' name='allday_bits[]' value='2' {$allday_bit2}>"._PICAL_MB_LONG_SPECIALDAY." <!-- <input type='checkbox' name='allday_bits[]' value='3' {$allday_bit3}>rsv3 <input type='checkbox' name='allday_bits[]' value='4' {$allday_bit4}>rsv4 -->
</fieldset>
</td>
</tr>
<tr>
<td class='head'>"._PICAL_TH_LOCATION."</td>
<td class='even'><input type='text' name='location' size='40' maxlength='250' value='$location'></td>
</tr>
<tr>
<td class='head'>"._PICAL_TH_CONTACT."</td>
<td class='even'><input type='text' name='contact' size='50' maxlength='250' value='$contact'></td>
</tr>
<tr>
<td class='head'>"._PICAL_TH_DESCRIPTION."</td>
<td class='even'>$description_textarea</td>
</tr>
<tr>
<td class='head'>"._PICAL_TH_CATEGORIES."</td>
<td class='even'>$category_checkboxes</td>
</tr>
<tr>
<td class='head'>"._PICAL_TH_CLASS."</td>
<td class='even'><input type='radio' name='class' value='PUBLIC' $class_public onClick='document.MainForm.groupid.disabled=true'>"._PICAL_MB_PUBLIC." <input type='radio' name='class' value='PRIVATE' $class_private onClick='document.MainForm.groupid.disabled=false'>"._PICAL_MB_PRIVATE.sprintf( _PICAL_MB_PRIVATETARGET , $select_private )."</td>
</tr>
<tr>
<td class='head'>"._PICAL_TH_RRULE."</td>
<td class='even'>" . $this->rrule_to_form( $rrule , $end_date ) . "</td>
</tr>
<tr>
<td class='head'>"._PICAL_TH_ADMISSIONSTATUS."</td>
<td class='even'>$admission_status</td>
</tr>\n" ;
It looks like plain HTML, doesn't it?