This is a constant question on calorie count site, which I used to participate in; it helped me lose 20-25 very stubborn pounds that my doctor wanted me to lose because I've long been prediabetic and was getting into the danger zone. I wasn't that overweight but diabetes runs strongly in my family. Even my thin relatives end up with it by their 50s and 60s. So if I don't want to go on insulin, I am told that I have to keep my weight within a very narrow range and be careful with diet and exercise.
Here is what I learned through that forum:
1) If you just diet only, you will basically shrink down to a smaller version of whatever shape you start at.
2) If you diet and do cardio only, it's pretty likely this is going to happen too - though you may make minor improvements in your shape, depending on what cardio you choose.
I'm proof: I ate a fairly low-carb diet (basically a diabetic diet), did no weight training but was running a lot, and doing yoga, and my measurements shrunk. I dropped 4 dress sizes. BUT the proportions all stayed *exactly* the same.... and I find that the 0p's have the exact same fit issues as the 6p's and 8p's did!!!
I may be the same exact shape - but my blood sugar and other numbers are much better and I feel better and my doctor is very happy, so I am embracing this shape!
3) If you take up weight training - and I'm talking heavy weights, not wimpy ones - not the machines but dumbells and barbells i.e. free weights - you can indeed change your body shape!!! Dramatically, depending on how much you do.
I forget the name of the book and web site, but it's some highly-regarded fitness challenge thing where they show these before and afters that are fascinating. Those who commit to the weight training program, end up in their "afters" all having basically the same shape: neither pear or apple. Hourglass is closest description; fit would be the best way to describe it. Like those fitness models you see on the late-night infomercials for fitness products. Proportional all over.
I used to do weight training and my body was definetly a different shape. I had much more of a butt (it's flat now) and better curves to my hips and thighs, balancing out my upper half. My waist was an inch thinner too, my arms thinner, and shoulders more shapely.
I dropped out of it due to various issues, and haven't gotten back into it because it takes a commitment I'm just not up to at this point in my life. Living at the gym just doesn't sound appealing to me anymore, and I can only do so much at home - no room here for a home gym. Maybe one of these days.
Can't answer your other question, because I'm an hourglass with inverted triangle tendencies.