In California can a living trust be revoked and relpaced with a new updated revocable trust of the same name?

Answer 1

Yes, assuming the trust was revocable in the first place. You need to prepare an Affidavit of Revocation naming/identifying the old trust and calling on the trustee to return and remit all assets back to the trustor. This should be notarized. Then you simply reverse the process by establishing a new trust granting the assets to the new trustee. This also needs to be notarized. As long as the creators of the trust, called the trustors, are still alive and possessing their full mental capacities, then they are in charge of the trust and can modify, amend or revoke the trust in part or in whole. Once one of the trustors dies, then at least their portion of the trust becomes irrevocable. When all trustors die, then the entire trust becomes irrevocable.
You can establish a trust that is irrevocable from the outset, in which case you better be sure you are doing the right thing and won't needing to be changing your mind about it. The assets placed in an irrevocable trust better be assets you won't be needing. They are being set aside for future purposes.

Answer 2

If it is a revocable trust, you can just amend it provided such powers were delegated within the original trust, without having to revoke and re-write a new trust, unless you absolutely want to replace the entire original trust.