Which parameters in the Bitcoin Core config file need to be set correctly prior to IBD? The majority of the parameters in the Bitcoin Core config file can be changed during or after IBD (Initial Blockchain Download) with no complications.

However, there are some parameters in the config file where it is important that you set them correctly prior to IBD. If you don't you will either have to restart IBD or it will greatly increase the time for IBD to complete.

Some parameters that need to be set correctly prior to IBD are testnet, regtest, prune and txindex as discussed here. Are there any others?
To my knowledge, the only parameters that have to be set before an initial block download are the regtest and testnet options.

Anything else, including txindex, can be altered later, although it may cost you a reindex or reindex-chainstate to enable functionality like a txindex if done after the block download has started.

Other parameters such as those governing the RPC, peers, and wallets can be quickly updated at any point.