octobercms - October CMS Modify the files in "modules" directory? -

i installed october cms, , have many questions. 1 of them is, want modify things in backend, , think files in modules/cms , modules/backend. so, question is, can modify files directly? or there better practice these case? perhaps way overwriting functionality without touch original files?

thanks.

of course bad practice modify core files! try use events or create patches.