The chaincode of the master private key is derived from a 256 bit seed following BIP 32:
https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki#user-content-Master_key_generationThe seed itself is discarded once the master private key is computed as it is extraneous information that is never used once the master private key is produced.
It is unclear to me what problem you are actually trying to solve. None of what you described makes any sense, and it seems like this is an
XY Problem. Please describe what it is you are trying to achieve, not what it is you think the way to the solution is.