By Default Magento Product Custom options has following field which have radio,checkbox,Multiple select,Select….so if we need to add new input type in that custom options so here is the code

Note : Make sure that Don’t disturb the Core Files always use Magento Standard

1) Open the file and copy in local folder

app/code/core/Mage/catalog/etc/config.xml

<multiplenew translate=”label” module=”adminhtml”>

<label>Multiple Select New</label>

</multiplenew>

2) Open the file and copy in local folder

app/code/core/Mage/Eav/Model/Adminhtml/system/config/Source/inputype.php

array(‘value’ => ‘multiselectnew’, ‘label’ => Mage::helper(‘eav’)->__(‘MultipleNew Select’)),

3) Open the file and copy in local folder

default/default/tempalte/catalog/product/edit/options/option.phtml

In this file you will found three case of multiple just above that

case ‘multiple’: //already there line 152

case ‘multiplenew’: //add above

case ‘multiple’: //already there line 211 

case ‘multiplenew’://add above

case ‘multiple’: //already there line 233                   

case ‘multiplenew’://add above

case ‘multiple’: //already there line 265

case ‘multiplenew’://add above

Note :Here Multiplenew is the new field

Clear the cache and run new input type will come.Hope this will help you!