Today, there are several GM crops that produce different proteins derived from Bacillus thuringiensis (i.e. Bt proteins). Some of the Bt proteins that we use provide protection from lepidopteran pests that feed on foliage, flowers, and grain (e.g. European corn borer, cotton bollworm). Different Bt proteins provide protection from coleopteran pests that feed on roots (corn rootworm). Within these two groups, industry uses a range of specific proteins to delay or overcome pest adaptation, as you suggest. For example, the Cry1Fa and Cry2Ab Bt proteins both provide protection from European corn borer, and insects that may develop resistance to one can be controlled with the other. Indeed, in most new Bt crops today, multiple Bt proteins are produced together specifically to combat emerging resistance. In the near future, we expect to see more new insect-protection traits in GM crops that will further ease the threat of resistance. Bt remains a rich source for those traits, and other mechanisms of protection, such as RNA-interference, are also being developed.
In regards to your second question, regulatory agencies around the world review each Bt protein individually for its human health and environmental safety. Even closely related proteins, such as those with just a few differences in their amino-acid sequence, are evaluated separately. What’s more, the safety of an existing Bt protein is re-evaluated when it is introduced into a new crop or even when re-introduced into the same crop at a different genetic position. That said, we have built up an enormous knowledge base around the safety of Bt proteins in general, which should make the evaluation of existing and new Bt proteins simpler, faster, and more robust.