Take your 4 string and lock it up for at least a few months and do not touch it till you feel good about your 5 stringer.
Keep in mind your 5 just adds B, while you still have EADG. So the only thing it will help you with as far as 'easy tuning' is the ablility to transpose down to D C and B standard tunings, and this may help you learn a bit about your fretboard. For ease with droptuning some people use hipshots, although drop tuning one string by ear should be a skill you should work on.
Finally, here is the best piece of advice I can give, if you are utilizing rocksmith as your primary learning source. Buy yourself a good amp combo, and run that between your bass and the game system. I can show you how if you need help, I do when I am jamming with my girlfriend for fun as she is just learning guitar. Turn down your bass volume settings in game, and just use your amp for your bass volume.
This will help you really hear what you are actually playing, and help you self critique your sound quality. As you know, just playing the right note at the right time is not all there is. The game uses simulated amp settings that tend to get lost in the mix, and you may feel you playing better than you really are. Doing this you can hear your ghost notes, how hard you are hitting the strings, and how and when to mute notes or let them ring along with other things. Especially with bass that game will let you get away playing quarter notes for eighth notes, and an amp will bring that out so you can hear it and fix it.
Best of luck to you, and like everyone says, don't rely on that alone, eventually lessons will help, but it will get you into and excited about playing which is a good thing, and build up your motor skills which is just as important as learning theory, but is just a piece of the puzzle. But just because the game says you know 99% of the song, does not mean you do. Your bass just had the right frequency at the right time. Really challenge yourself and don't get lulled into a false feeling of accomplishment.