CocoaPods use locally modified Pods
Oh. It was right in the documentation here.
pod 'YourCustomPod', :path => 'relative/path/...'
In this case you'll miss the future updated from the library which might be bug-fixes or future updates
There is another way in which you can customise it as well as update it in future
Here is an article which i have written explaining the same.
https://medium.com/@mihirpmehta/how-to-modify-cocoapods-library-within-pods-647d2bf7e1cb