Hi Sushanto,

In order to change the Object Permissions in one or more profiles, you will have to first retrieve the object along with the profiles.

For instance, my package.xml to retrieve the files will be as follows:

<?xml version="1.0" encoding="UTF-8"?>
<Package xmlns="http://soap.sforce.com/2006/04/metadata">
    <types>
        <members>Test__c</members>
        <name>CustomObject</name>
    </types>
    <types>
        <members>*</members>
        <name>Profile</name>
    </types>
    <version>27.0</version>
</Package>

This will give me all the Profiles metadata along with the object (Test__c).  If i open any profile metadata file, this is how it looks.

<?xml version="1.0" encoding="UTF-8"?>
<Profile xmlns="http://soap.sforce.com/2006/04/metadata">
    <fieldPermissions>
        <editable>true</editable>
        <field>Test__c.Contact__c</field>
        <readable>true</readable>
    </fieldPermissions>
    <fieldPermissions>
        <editable>true</editable>
        <field>Test__c.Opportunity__c</field>
        <readable>true</readable>
    </fieldPermissions>
    <fieldPermissions>
        <editable>true</editable>
        <field>Test__c.User__c</field>
        <readable>true</readable>
    </fieldPermissions>
    <objectPermissions>
        <allowCreate>false</allowCreate>
        <allowDelete>false</allowDelete>
        <allowEdit>false</allowEdit>
        <allowRead>false</allowRead>
        <modifyAllRecords>false</modifyAllRecords>
        <object>Test__c</object>
        <viewAllRecords>false</viewAllRecords>
    </objectPermissions>
    <userLicense>Salesforce</userLicense>
</Profile>

In the profile file, you will have to change the values under <objectPermissions> tag. Once saved, you can then deploy the profile along with the object file. You can use the same package.xml file, you used to retrieve.

Hope this helps. Let me know if you have any queries.

Regards,

Satish Kumar

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