we have a meta tags [plugin that allows you to add meta tags for the home page and it will not get updated based on the subdomain change, for example if the meta tags for the home page is
<title>buy samsung mobile in India, rent a bike in India</title>
<meta name="description" content="buy samsung mobile in India. discussing, organizing, and meeting people near you."/>
<meta name="keywords" content=" house for rent, house for sale, house rentals, sell and buy,used mobile in India"/>
<meta name="title" content="buy samsung mobile in India, rent a bike in India"/>
and for subdomain (ex [login to view URL]) i can be able to give a completely new meta tags for subdomain and the city name should get automatically change based on subdomain change
for example
<title>buy used samsung mobile in bangalore, buy used bike in bangalore</title>
<meta name="description" content="buy cheap samsung mobile in bangalore. buy used mobile spare parts near you."/>
<meta name="keywords" content=" house for rent in bangalore, house for sale, house rentals, sell and buy,used mobile in banagalore"/>
<meta name="title" content="buy used samsung mobile in bangalore, buy used bike in bangalore"/>
the city bangalore should be automatically changed based on subdomain change ex [login to view URL],com , then the meta tag should show pune in place of bangalore. like wise for all
so you need to create two sections one for main home page and another section for subdomain city based meta tags
or you can create only for subdomains as the meta tags for main home page is already present , your modification should not affect the main page tags.
you should have complete knowledge on osclass and integrate or create a plugin