I think you only need
classes/product.php
admin/tabs/AdminImport.php
In AdminImport.php you need to add your fields at line 184:
Just Like:
'condition' => array('label' => $this->l('Condition')));
At Line 936
$id_product_attribute = $product->addProductAttribute((float)($info['price']), (float)($info['weight']), 0, (float)($........
you have to add your fields with
...(int)($info['default_on']), ($info['YOURFIELDNAME'])...
Watch out that you fit the addProductAttribute function in Product.php.
In Product.php go to line ~920
public function addProductAttribute...
and add your parameters in the right position
.., $yourfieldname, ...
Now edit the Array in the function
array('id_product' =>.....
add your field with
..., 'yourfieldname' => pSQL($yourfieldname),...
This works for me. At the csv import your have to choose your fields at import step 2 manually.
Wrote this down in 5 minutes, hope it helps anyway..