The SAP Service (SAPPRD_00) copies the contents of the environment variables to the registry from the user it finds registry value HKEY_LOCAL_MACHINE > SOFTWARE > SAP > SID, key AdmUser = DOMAINsidadm, before startup. This needs to be adapted as well. In addition, the new <sid>adm user needs all environment variables as the original <sid>adm user. The environment variables and registry values (which are overwritten during each start-up) are a necessity to get SAP up and running.
This was first published in October 2007