The change is in 1 week. I think if we do not get a path by that time, we should consider removing the German chart of account as it will be clear that no one is maintaining it.

The draft of the Federal Ministry of Finance [1] confirms under 2.3 the tax codes to be used like the document of msg58739 suggests. So I think we can be sure that it will be handled this way.

[1] https://www.bundesfinanzministerium.de/Content/DE/Downloads/BMF_Schreiben/Steuerarten/Umsatzsteuer/2020-06-12-befristete-Senkung-umsatzsteuer-juli-2020.pdf?__blob=publicationFile&v=3

Please note that it is planned to pass the law for this change on 2020-06-26. For now it is just a plan. So there is still some uncertainty.

This site[1] says that the tax authority told them that the new taxes need to be declared on the following tax codes:
 * tax_code_35 (xml_id) for base
 * tax_code_36 (xml_id) for tax

For intra community acquisition the tax codes will change to 
 * tax_code_95 (xml_id) for base
 * tax_code_98 (xml_id) for tax

Unfortunately i was not able to find the original source of this information.

[1] https://rechtlogisch.de/elster-eric-news-13-keine-aenderung-der-ust-va-und-uste-formulare-wegen-steuersatzsenkung/

One point that should be verify is that the tax during the reduced period would be reported in the same tax code and account.

On July 1st 2020, the VAT rates in Germany will be reduced until 2021: https://www.reuters.com/article/us-health-coronavirus-germany-economy-idUSKBN23J16Y
We need to update the tax definitions to get 3 children taxes: one for each period (before, during, after) for the taxes with 19% -> 16% and for 7% -> 5%.
Similar change has already happened in account_fr, see rev 58c224a204b3