I don't recommend trying to crack the bodies open unless there is already a gap in the seam that you can get a blade or screwdriver into and even then be very careful of flying parts/blades if/when it does break apart.
I am quite a guy from the 'old school' and I tend to crack the bodies open. This gives me the opportunity to better work on the adaptation of the body for a different head/limb, and ensure the same level of articulation as the original figure.
In the case of JLU I agree with Jim_Abel that it is better to choose bodies which have some gap to use as start. Be specially careful with female bodies, as they are more fragile.
My recomendation for people with not a lot experiencing in 'cracking bodies' is:
- Use a blade only if a tiny flat screwdriver cannot get the job started. That is, use the blade just to start creating the gap, but switch to the screwdriver the sooner the better.
- Actually it tends to be better to use two screwdrivers: one keeps the gap open while you extend the gap with another
- observe carefully the plastic arround the gap you are trying to open. If some white lines appear this may mean that it is about to tear there.
- Usually the body has 2 to 4 pegs inside connecting the front and back parts of the body. If you are lucky sometimes these are not glued and make no force against opening the body, but sometimes they do. In extreme cases, the blade has to be used to cut them loose. But be careful with this step.
- It is usual that the borders where you placed the screwdrivers deform a little (taking the screwdriver's shape). This can be sanded down or fixed later.
Bryan Long wrote:
Second warning: Superglue often creates a whitish residue around the glued area that needs to be repainted or cleaned off. Try to make darn sure the glue doesn't ooze out of the neck join.
Actually the same applies in the 'cracking body' method, when trying to join the torso halves back into one. Superglue is great, but you have to make sure you it does not spread into the articulations. A trick: if it does, keep moving the articulation(s) affected while the glue has still not hardened. You may need 2 minutes of limb moving to make sure it does not get stuck, but it is worth the effort.
For those that cutt heads and stick a new one, please be very careful with the glue, as sometimes it tends to arrive to the shoulders' articulations, specially in the small female bodies. If that happens use the trick I just explained to avoid articulation lost.