Generating SHA256 cert from SHA512 intermediate

We need to create a SHA256 hashed certificate from an intermediate SHA512 hashed cert. We use RSA and if we specify KeySize 2048 our cert is RSA(2048) and signed with SHA512.
As I understand this from csr.go:
`case kr.Size() >= 2048:
return x509.SHA256WithRSA`
It should be specified to use SHA256.

Is there a way to force the signing algorithm?

Start with the algorithm-selection logic in csr.go, especially the RSA key-size case shown in the issue. Determine how certificate signing algorithms are currently selected and whether the requested SHA256 choice can be exposed; done when the supported behavior for RSA certificates is clear and covered by the relevant tests.

Written by the indexing model from the issue text.