One more datapoint. When I tried migrating/upgrading a chain on `Geth/v1.7.3-stable-4bb3c89d` to `Geth/v1.8.13-stable-225171a4`:
* new contracts can be deployed on `Geth/v1.8.13` after migration
* web3 «set» transactions can be executed without errors on contracts that were deployed on `1.7.3`
* web3 «get» transactions fail with `Error: Couldn’t decode uint256 from ABI: 0x`. Unfortunately, this requires the change to set `homesteadBlock: 0`
Is there any way to «update» genesis config before/after migration (rolling or otherwise) without having to lose chain data?