SetOptions

SetOptions[s,name1->value1,name2->value2,…] sets the specified default options for a symbol s. 

SetOptions[stream,…] or SetOptions["name",…] sets options associated with a particular stream. 

SetOptions[object,…] sets options associated with an external object such as a NotebookObject or CloudObject. 

Please visit the official Wolfram Language Reference for more details and examples on core symbols.