Text Component Modification

you can add default components to parsys by adding child node at the template level, check this OOTB example which is /apps/we-unlimited-app/templates/article/jcr:content/par/article

In your case, you need to add title component as a child node of the parsys

/app/your-project-name/templates/your-templates-name/jcr:content/name-of-the-parsys/title

When you create a page using the template by default the title component will appear on the page.

Did u mean that few of the fields of your title component should be mandatory for one set of pages and optional for other set of pages ?

Yes for few set of pages, fields under title component is mandatory, for rest its optional.

I assume you are referring to core components - you can override core components. See this HELPX artilce as an example of how to override a core component - Extending Adobe Experience Manager Core Components (this is an example of how to override a core component)

smacdonald2008​

    What he wants is lets say he has a title component with 3 fields in dialog. He want 2 field to be mandatory in Page 1 and optional in Page 2 . So its more like handling a field's required property depending upon the templates

Are these components are default components on the page ?

If these components are default components then you can follow the same approach whatever I have mentioned earlier by adding by adding a required property to the component node.

If not default components then you write javascript which finds template type and based on that it will dynamically add the required property. it requires some R&D and Javascript knowledge

The simple and easy approach creates another version of the text component v2 that contains mandatory fields, but you need to convince the client on this.

For a component, when you save a dialog.. write a listener and have a validation in place based on the resourceSuperType of that page. However as Rajas mentioned you need to have experience in JS to handle this.