Create custom template for outlook compose mail

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Outlook

VBA

AddIn

Hi,
I have designed one custom form in outlook which have To, CC, Subject, default properties and in addition my new custom properties like Category, Sales Type, Location. and i have also published this form. I want this custom form template should get loaded on clicking new mail in outlook.
i.e.I need to override default outlook new mail template.

What I have tried:

I tried Walkthrough: Creating Your First VSTO Add-In for Outlook[^]
This only allows to set values of default properties like subject and boby.
But I need to add and display new properties also which i have mentioned in description.

I have also checked for https://www.add-in-express.com/creating-addins-blog/2011/08/19/how-to-add-a-custom-property-to-the-userproperties-collection-of-an-e-mail-item-in-outlook/
But in this example, new property is getting created which can be seen if you click on design a form option. but this new property in not getting loaded/visible in template