NOTE: I am aware that we can change this name from the Email template setting, but I'm trying to accomplish this through code. 

First, I overrided the PDF name when printed directly from the Print --> Quotation/Order by overriding the <report>...</report> tag for the id="sale.action_report_saleorder" and  successfully changed the name of the PDF using the print_report_name attribute.

However, when we try to send the quotation to the customer using 'Send By Email', the PDF which is attached gets the default name and not the overrided name. 

I tried to override the contents of "email_template_edi_sale" in a new file, however it is wrapped in a <data noupdate=1> attribute:

<record id="email_template_edi_sale" model="mail.template">

    <field name="report_name"> New-pdf-name </field?

</record>

So my question is, how to change the name of the quotation/SO file which is attached in the 'Send By Email' wizard?