So I have an offline wallet created with Electrum. When signing transactions on the cold storage machine, I would like to be able to check that the address I'm sending the change to is actually a change address I own, however since Electrum is offline it's not up-to-date with which addresses have been used, and so the next change address that is used in the transaction hasn't actually been created yet.

For receiving addresses, I was able to manually create these addresses by running:

>> wallet.storage.put('gap_limit', 50)
>> wallet.storage.write()

in the console, which generates 50 rx addresses worth of keys.

However, this only generates receiving addresses, and I have funds in change addresses beyond the 6 that are generated by default. Unfortunately I haven't found how to increase this gap limit for change addresses. I've tried looking through the electrum source but haven't found anything that would let me change this.