PROB §19104: (a) Subject to subdivision (b), if a claim is filed within the time provided in this chapter, the creditor may later amend or revise the claim.

(a) Subject to subdivision (b), if a claim is filed within the time provided in this chapter, the creditor may later amend or revise the claim. The amendment or revision shall be filed in the same manner as the claim. (b) An amendment or revision may not be made to increase the amount of the claim after the time for filing a claim has expired. An amendment or revision to specify the amount of a claim that, at the time of filing, was not due, was contingent, or was not yet ascertainable, is not an increase in the amount of the claim within the meaning of this subdivision. An amendment or revision of a claim may not be made for any purpose after the earlier of the following times: (1) The time the court makes an order approving settlement of the claim against the deceased settlor under Chapter 2 (commencing with Section 19020). (2) One year after the date of the first publication of notice to creditors under Section 19040. Nothing in this paragraph authorizes allowance or approval of a claim barred by, or extends the time provided in, Section 366.2 of the Code of Civil Procedure.