::: warning 🚧 OP Stack Hacks are explicitly things that you can do with the OP Stack that are *not* currently intended for production use
OP Stack Hacks are not for the faint of heart. You will not be able to receive significant developer support for OP Stack Hacks — be prepared to get your hands dirty and to work without support.
:::
OP Stack blockchains have a number of [predeployed contracts](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/src/constants.ts) that provide important functionality.
Most of those contracts are proxies that can be upgraded using the `proxyAdminOwner` which was configured when the network was initially deployed.
The predeploys are controlled from a predeploy called [`ProxyAdmin`](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/contracts/universal/ProxyAdmin.sol), whose address is `0x4200000000000000000000000000000000000018`.
The function to call is [`upgrade(address,address)`](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/contracts/universal/ProxyAdmin.sol#L211-L229).
The first parameter is the proxy to upgrade, and the second is the address of a new implementation.
For example, the legacy `L1BlockNumber` contract is at `0x420...013`.
To disable this function, we'll set the implementation to `0x00...00`.
We do this using the [Foundry](https://book.getfoundry.sh/) command `cast`.
1. We'll need several constants.
- Set these addresses as variables in your terminal.
require.Equal(t,expectedL1Origin,verifier.SyncStatus().SafeL2.L1Origin.Number,"L1 origin is forced in, given enough L1 blocks pass by")
require.LessOrEqual(t,miner.l1Chain.GetBlockByNumber(expectedL1Origin).Time(),engine.l2Chain.CurrentBlock().Time(),"L2 time higher than L1 origin time")
require.LessOrEqual(t,miner.l1Chain.GetBlockByNumber(expectedL1Origin).Time(),engine.l2Chain.CurrentBlock().Time,"L2 time higher than L1 origin time")
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