Hi, you can change the 'Marks' to 'Score' by going into the language edit screen - search for the text strings that contain 'marks' in the Quiz modules, enter the text that you want and save the language.
It will not require any edits of the core code... only the language text gets changed. For example if you want to change 'Time taken' to just 'Time', find the string containing 'Time taken' and enter 'Time' in the corresponding box and save it.