The angles are the same. Remember this. What differs is how it looks from your perspective when down on the shot. Practicing on a 7 footer or ANY table for that matter cannot be a bad thing. With that said, if your 7 footer has big easy pockets you might be able to make shots that would normally miss on a tighter 9 foot diamond table. Be aware of this. If you throw a ball in the length of the table with tons of english on your 7 footer that hits the long rail before it pockets, take note of the fact that you probably would have missed that shot on a 9 foot, tight pocket, super "live" rail table. Any time you don't hit dead center of the pocket take note and remember that you could have, and should have hit that better. Snooker players play on a 12*6 table with ridiculously tough pocket rails. Their entire game is hitting DEAD center of the pocket. If you can do that on a 7 footer you can do it on a 9 footer. You just need to step back from the table and see the angles like you would on your 7 footer. It will look different from the perspective of shooting, but if you focus on the contact point of the object ball you should be able to make the shot regardless of the table size.
Bottom line is don't settle for anything but middle of the pocket when you are playing on a 7 footer unless the shot calls for you cheating the pocket. If you are cheating the pocket make sure you hit it exactly where you want to. If you don't, take note and try and do better next time. This will translate to your 9 footer game. It's very easy to "miss" a ball on a 7 footer and still make it. Think of these as misses and try and do better.