Quote from: ChapInRed on May 19, 2023, 09:38:08 PM

I was not aware of the change address mechanism, so please help me clarify:
- small (test amounts) outgoing transactions from my old wallet will use a change address from my keypool
- Bitcoin Core is offline so won't know about change returned
- I presume that once I sort my Ledger Wallet, the blockchain will link all change transactions to it?

Bitcoin Core will select a suitable UTXO to spend for that transaction, then if there's an excess amount of BTC, it'll send it to one of your address (change address).
All those are included in that single transaction.
Here's some basic info about how Bitcoin transaction works: learnmeabitcoin.com/beginners/transactions#
When you broadcast the transaction to your node's mempool, even offline, it'll be able to include that change to your available UTXO so you can spend it in your next transaction.
The minor issue here is the time gap between the small test transaction and your next actual transaction because it has a default expiration of 14days;
but even after expiration, you can always rebroadcast it to your offline node's mempool before sending the actual transaction.
I don't get what you mean by "link" but all it has to do is to sync to the blockchain to see if any of its keys can spend your coins.

Quote from: ChapInRed on May 19, 2023, 09:38:08 PM

getwalletinfo for my old wallet returns: walletversion=10500, format=bdb, txcount=6, keypoolsize=1000

Oh, so Bitcoin Core updated your old wallet's keypool, "keypoolsize=1000" ensures that the concern about the change address wont happen.
Because your wallet already reserved 1000's of addresses.

Since it's not HD, it's a good decision to create a backup of your current wallet.dat to be on the safe side since the newly generated keys aren't included in your old backup.
Although those wont be used in the two transactions that you'll create.