I have an Xcode workspace that uses CocoaPods to include several third-party frameworks. I would like to edit a line of source code within one of these dependencies. However
You can not make changes in Original Pod file. If you want to add some more features then you have to fork that particular repo.
Follow steps to do so :
pod 'GPUImage', :git => 'https://github.com/UserName/GPUImage.git'
You can create Category (Objective C) or Extension (Swift) to extend or add some features to existing class.