What are ways to calm new parents who are really frustrated so they can avoid hurting the baby or causing shaken baby syndrome?

Provide support. It is important that new parents have a support network of friends and family. If that network can commit to helping in various ways like prepping meals, housework or watching the new baby this can go a long way in preventing a tragic outburst or excessive frustration. For sleep deprived parents, the opportunity to nap is especially welcome.
Anger management. The degree of shaking necessary to damage a baby is quite severe and must occur repeatedly to be really damaging. Most new parents can be angry with the baby, but will easily diffuse the anger and avoid injury to the child. Normal play and enthusiastic handling of the baby will not produce brain damage.