Dynamic modification of an Iceberg group during an open Lightning channel

Determine how much an Iceberg threshold-signing group can change its internal configuration while a Lightning channel remains open, including proactively refreshing shares, repairing the share of a member that has lost it, changing group membership, or changing the threshold, while preserving the aggregate funding key.

Background

Iceberg fixes an aggregate public key for the threshold group, and that key occupies one participant slot in the channel’s MuSig2 funding key. Consequently, changing the aggregate key would require closing and reopening the Lightning channel. The paper explicitly leaves unresolved which internal maintenance and reconfiguration operations can be performed without changing that aggregate key, including share refresh, recovery of a lost share, membership changes, and threshold changes.