How often should I shake things up? Changeing diet & workout routine

Since February I have been undergoing a major lifestyle change. Diet is high protein, mid carb. low fat lower, even lower sodium diet. ( Think body builder) and 3 days a week weight training with a trainer. I have lost over 30lbs, gone from a 16 to a small 10 and look almost as good as I did when I got married.

I have been on my own since beginning of July and have been doing well. My weight is maintaining and I have not gotten flabbier so far. I am ready however for a change. I have read and Love the New Rules of Lifting for Women and want to make some diet and lifting changes to my program.

My question is: Do I take this a week at a time and substitute a current exercise with a new one until I have gradually changed over. Same for the diet: I am so afraid adding in dairy and peanut butter will send me spiralling backward, I am hesitant to try.

Any thoughts?

edit ( change title for responses)

 Most such training programs are designed to function as a whole, so your best bet is to simply start the training program as is. The dietary guidelines are somewhat more forgiving it seems, at least there are several posters here who've had a lot of success with NROLW without following the diet plan, just sticking to the CC basics. 

 You can give it a try with just a little bit and see how you respond when adding in other foods to your dietary regime - I don't think it matters as much if the changeover is abrupt or not. And if taking it slow gives you peace of mind, that makes it clearly better for you regardless.

Thanks Melkor,

Will change over weight training this week and work in new foods gradually.