okay, first of all, i dont know what you meen by 'how safe is it'
whenever you perform any kind of mod you take a risk of fuckin your box over, and on that note its not safe.
now, if you want me to help you, i am going to need more info! what kind of exploit did you use to mod? slayers will install evox ( a dashboard that will allow you to run apps, games, trainers, emulators ect.) and yes, you will be able to copy games to your hdd but not many with your stock hdd (you will need a program like dvd2xbox) found in the usual places.