Regarding creating templates (fetching and populating child tables

I am looking to implement Quotation Item template, like the tax template. I have prepared a custom doctype Quotation Item Template that has a child table which contains list of Items. On quotation whenever i select the template from a link filed i want it to populate the Quotation Items by copying from the template child tables.
I’ve looked around and found it’s possible with APIs and modifying the code base. But just curious if it’s possible to implement using client/server scripts so that I avoid updating the code base.
The goal is to make creating quotations more fast and efficient with templates. Duplicating an existing quotation is an option too but if I can do this with script its a good customization tip that i can use on other parts of ERP.