Can a court require an executor's bond to be increased later if the estate's value grows during administration?

Yes, a bond amount isn't necessarily fixed forever at whatever figure applied when the trustee was first appointed. Because a bond is meant to reflect the value of assets the trustee is actually responsible for, a court can require it to be increased later if the estate's value grows significantly during administration — for example, if a major asset is sold for more than expected, or new assets are discovered or received well after the original bond was set.

This isn't something that happens automatically without anyone raising it; it generally requires the issue being brought back before the court, whether by the trustee themselves proactively flagging a material change in estate value, or by a beneficiary or other interested party asking the court to revisit whether the existing bond still adequately protects the estate given its current value.

Because the whole purpose of a bond is to match the actual risk being protected against, letting it become badly out of step with a much larger estate defeats that purpose. Trustees managing an estate whose value has changed substantially since the original bond was set should raise the question with their lawyer rather than assuming the original figure remains adequate indefinitely.