I am using 'tap-salesforce' extractor to pulls data from Salesforce. I want to customize the behavior of this tap to get data as per my requirement. Should i modify 'tap-salesforce' extractor to meet my requirement? or Is there any approach to create my custom tap to customize a parent tap? What should be the best approach?

Depends what your requirement is, and whether the tap configuration can/could feasibly accommodate that. Generally speaking, I think the best approach is forking the plugin repo and updating the

pip_url

(and then

meltano install --clean extractor tap-salesforce

), since it gives you the most control.