So i just beat the game on apprentice. i got the apprentice achievement and all went well. so if i want to beat it on sith master then do i have to start a whole new game or can i start at the beginning with the same profile but just change the difficulty so i can go through the game on sith master with a bunch of high stats and what not.

You can CONTINUE a game once you have beat it. That-a-way you can keep all of your stats, costumes, crystals, ect. You have to change the difficulty in the beginning and you cannot change it at all during the game.

Apprentice ---> Sith Master is a huge leap. I have beat the game like 4 times and cannot muster up enough courage to even try Sith Master. ;)

I started out with 'Sith Warrior,' but found many of the bosses were just too difficult to beat, or I just didn't want to waste the time, so I used 'Apprentice only as necessary and got NO achievements at all. Now I'm using Sith Lord and will try to get three achievements in one run-through. I can't believe how many times I died already.

Go with Sith Warrior for now unless you want to be bold and try the 'Lord difficulty'. You'll get all the achievements of 'warrior' as well.

you can change the difficulty on your current playthrough, but it won't get you any achievements

what i did was max out all my stats on Apprentice, then played that file through on Master to get a feel for it. By the time I started a new file to get the Master, Lord, and Warrior achievements, it went by easier since i'd gotten used to the difficulty level with a stronger character.