Can a POA be changed without the elderly present?

My understanding is that It depends on what the existing POA states. If there is a successor listed on the original POA then the elder doesn't have to be present. The elder would have already made that decision.
Needless to say, if the elder is capable to appoint a new POA then it's always prudent to have a secondary listed. If the elder can no longer appoint a POA, then guardianship might be the next step. Speak to an elder attorney in your state.

No. It must be granted by the elderly person and they must be of sound mind and in person.