Inherit the res_partner model and add in defaults customer: False.

You don't have to edit in the crm module. First create folder in the addons folder, name it as partner_customization. Then in that folder create 2 files named __init__.py and __openerp__.py. Then in __init__.py add the line:

import partner

then in __openerp__.py add the following:

{
    'name': 'Partner Customization',
    'version': '0.1',
    'category': 'Custom',
    'description': """
    """,
    'author': 'Gopakumar',
    'depends': [
        'crm'
        ],
    'init_xml': [],
    'update_xml': [
    ],
    'demo_xml': [],
    'test': [],
    'installable': True,
    'active': False,

}

Then create one more files named partner.py . Then in partner.py add the following:

from openerp.osv import fields, osv

class res_partner(osv.osv):
    _inherit = 'res.partner'
    _defaults = {
    'customer': False
    }

Then restart the server, then update the module list and install the new module.