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No it's not, otherwise Blocktrades wouldn't talk about changing it via a hardfork. The yield for HBD in savings is a setting for witnesses. Maybe you mistaken them because they are both currently set at 10%.

I meant it should be coded as a witness variable in the upcoming hardfork so it can be quickly adjusted as needed.

You are correct. Not sure if it should be added as a witness parameter though. Kind of sensitive stuff (although so is the price feed and others), but yet again maybe I'm paranoid, we've been through JS takeover and puppet witnesses.