If I create an RBF transaction using the Qt GUI but specify my own custom change address, bumpfee doesn't work because it claims it can't find the change address:

    "Transaction does not have a change output"

This is because none of the outputs satisfy

    pWallet->IsChange(...)

I see there's a "TODO" commented in `CWallet::IsChange()` in `src/wallet/wallet.cpp`:

    // TODO: fix handling of 'change' outputs. The assumption is that any
    // payment to a script that is ours, but is not in the address book
    // is change.

I tend to put all my addresses in the address book whether I'm going to use them as change or not. I guess if the wallet was capable of creating its own SegWit change addresses I'd stop using custom change addresses, but currently it always seems to send change to a legacy address if I don't manually specify a change address.
{ "send", 4, "include_unsafe"},
    { "send", 4, "minconf"},
    { "send", 4, "maxconf"},
    { "send", 4, "add_to_wallet"},
    { "send", 4, "change_position"},
    { "send", 4, "fee_rate"},
    { "send", 4, "include_watching"},
    { "send", 4, "inputs"},
    { "send", 4, "locktime"},
    { "send", 4, "lock_unspents"},
    { "send", 4, "psbt"},
    { "send", 4, "subtract_fee_from_outputs"},
    { "send", 4, "conf_target"},
    { "send", 4, "replaceable"},
    { "send", 4, "solving_data"},
    { "sendall", 0, "recipients" },
    { "sendall", 1, "conf_target" },
    { "sendall", 3, "fee_rate"},
    { "sendall", 4, "options" },
    { "sendall", 4, "add_to_wallet"},
    { "sendall", 4, "fee_rate"},
    { "sendall", 4, "include_watching"},
    { "sendall", 4, "inputs"},
    { "sendall", 4, "locktime"},
    { "sendall", 4, "lock_unspents"},
    { "sendall", 4, "psbt"},
    { "sendall", 4, "send_max"},
    { "sendall", 4, "minconf"},
    { "sendall", 4, "maxconf"},
    { "sendall", 4, "conf_target"},