DO be safe
Dremels and heat guns make repositioning easier, but it also makes it more dangerous (especially for a clutz like myself). Handily, it doesn’t take too much of an investment (just some creativity) to protect yourself.
No matter how careful you are, cutting plastic results in flying bits and nasty dust. Protect your eyes from harm with a pair of goggles, often available second hand for cheap- check garage sales and thrift stores. Keep the plastic dust out of your lungs with a dust mask. Sure, you can buy those little white face masks, but I prefer the bandit look for economy and style.
When using a heat gun, plastic pony parts can get really hot, but you need to maintain dexterity in your fingers to accurately manipulate the heated plastic. That’s why I opted for a thick pair of socks on my hands to protect myself from burns.
Bottom line: I look totally ridiculous when I’m customizing.
DON’T bend without reheating
Sometimes I’m tempted to rebend a body part when it’s only a little warm. But the plastic that was totally malleable a few moments ago is now brittle, and the same little bending motion will snap it. Trust me. (See also: How to Fix a Broken Leg and the upcoming How to Fix a Broken Leg at the Joint)
DO heat the big areas first
When using heat to bend plastic, you always want to make the biggest changes first. Big chunks of plastic need more heat to become soft and bendy. If you heat and shape a small area, like an ear, and then move on to a nearby large area, like the model’s neck, your perfectly formed ear will become a blobby mess while you struggle to heat the neck. Even if the ear gets a little limp, you won’t be ruining previous work.
DON’T loose the little pieces
It’s easy to get caught up in the hacking and bending and chopping and loose a little piece, especially when you’re working on a small scale. Keep track of all the bits in a container of some kind. It’s a simple enough idea- and certainly simpler than resculpting a lost leg from scratch.
DO consult your references
I’m so busy gathering my heat gun and safety gear and pliers and dremel and bits and superglue that sometimes I forget to grab my reference. But a reference is crucial when you’re making big sweeping changes like hacking off a head or moving legs. You always want to keep your main reference handy so that with each cut or bend you progress towards your final goal, and avoid incorrect angles or unnecessary work.
And most importantly… DO try your hand at repositioning! It’s a jolly good time.