[Nauman]

Custom fields are just that. Fields that have been added to the standard Salesforce schema to tailor the data for each object. The user who creates the field can specify the field type and any applicable limitations, such as the maximum number of characters in a text field. These fields might be added to an Org via a managed package or through direct customization.
Standard fields in contrast are those that are already present in the Salesforce schema when a new Organization is created. They are present in all Orgs where the same features are enabled. You can't customize these fields to the same degree. E.g. you could change the display label, but not the underlying API name or data type.

[Nauman]

Which Salesforce edition are you using?

[Nauman]

This example shows Apex to create an ApexPage, but from python it will be a matter of sending the request to the correct endpoint.

You'll need to send a JSON payload to the correct enpoint with the correct details, for ApexTrigger see here: http://www.salesforce.com/developer/docs/api/Content/sforce_api_objects_apextrigger.htm

private void setRestPostUrl(){
String sfdcUrl = (String)URL.getSalesforceBaseUrl().toExternalForm();
String apiPath = '/services/data/v30.0/sobjects/ApexPage';
restPostUrl = sfdcUrl+apiPath;

}

sfdcURL would be: "naXX.Salesforce.com", where XX is the instance (na1, na2, na3...)
apiPath: the last part 'ApexPage' is what you'll need to modify. For Triggers: ApexTrigger, for classes: ApexClass.

So you'll need your OAuth token, and send your payload to: https://na10.salesforce.com/services/data/v30.0/sobjects/ApexTrigger
(You'll set a Header as 'Authorization' with the OAuth token.)

[Nauman]

gd points.. I remember a couple years ago a similar problem was the talk of the town for sometime.

Though I am not really sure how it was tackled as I was not directly involved into it..

[Nauman]

Yes i had added the app in the navigation menu of salesforce1

[Nauman]

As per the http://www.salesforce.com/us/developer/docs/apexcode/Content/apex_bulk_sharing_understanding.htm

it is not possible. "All implicit sharing added by Force.com managed sharing cannot be altered directly using the Salesforce user interface, SOAP API, or Apex"

Howsoever, the work-around is this:

You need to change the Sharing Rule which is causing the share. which is to delete a record with Sharing type Rule

If(Trigger.IsUpdate){
List<OpportunityShare > sharesToDelete = [Select o.UserOrGroupId, o.RowCause, o.OpportunityId, o.OpportunityAccessLevel, o.Id From OpportunityShare 
where RowCause=:Schema.RowCause.Your_Sharing_Rule__Here and o.OpportunityId='######'];
}

And then do this:

if (!sharesToDelete.isEmpty()) {
delete sharesToDelete;
}

[Nauman]

That helps @prafull