Attn web3 builders: if your smart contracts are upgrade-able, it has a backdoor [period]. While, I respect your personal design choices with upgradeability, it's worth including a disclaimer/mention around this to your community (includes non- technical ones) to avoid inaccurate assumptions regarding decentralization.

Alternatively, you always have the option of writing newer versions of your smart contracts that your community can be given a choice to migrate to. 
Although this means a bit of end-user friction, it is a path that's more secure, decentralized and offers the community a say on this.