Hello Sir
I am having 1 year of experience in Magento, I can work in theme installation to code customization, Extension installation, product management etc.
Here are my suggestions to increase score in Yslow:
1) some 3rd party js/css are not set for Expires Heders, we can do it by just creating a local file with that content,
2) Combine Js / css in Magento.
With these steps I think score will be increase up to 85% from 76%.
So with these steps, yes I can do this.
Thank you.