how to configure bitcoin-core (bitcoin-qt) to not use change addresses? Can bitcoin-core wallet be configured to not use change addresses, but just one address?

If yes, how? Thanks

(PS: I know most people will try to convince me that this is not a good thing, but I have perfect valid reasons. I know the privacy implications of this, ok? :)
It's unclear what you want.

Do you want no change addresses, but still have change that goes back to one of the addresses from which coins were taken? That does not have any size/fee benefit. This is possible by using the coin control feature (in the Bitcoin-Core GUI) or the createrawtransaction RPC interface.

Do you want no change at all? That means the amount you are sending must exactly match the sum of the sizes of some of the unspent outputs you have in your wallet. It does result is slightly smaller transactions and thus lower fees, but it is highly constraining. You'll have to construct transactions manually if you need this.