I can understand wanting the default Google Maps app back. Maybe, the new one has superb turn-by-turn. But I cannot understand wanting the old YouTube app back... it was absolute trash, being unable to play a good chunk of YouTube's content due to there being no advertising in-app. This request seems more pointless proof of concept than anything, and a good way to brick your iPhone.
On the constructive advice front, you could theoretically find an iOS 5 artwork compilation and move the appropriate images over (ie for Phone.app and... the other stuff). I don't think anyone's mastered the pre iOS 6 silver status bar, but Blackout in Cydia allows a permanently black one. You can also use a number of tweaks to hide apps (like Passbook and Apple's Maps) from Springboard, SBSettings and Springtomize come to mind. And for the record, I have Google Maps set to be my default maps application using Browser Changer. I only use Apple's Maps rarely when Google gives me incorrect directions (because yes folks, this does happen).
Best of luck, I guess.