Hello. You are right, if it ain't broke.... This is what happened:
serverclass= SASHELP.EMCORE.EMCODETOOL.CLASS
This indicates a tool built on the foundation of the EM code node. This is valid for EM 5.3, EM 6.1, and beyond, so there is no backwards compatibility problem. In addition, the experimental extension tool functionality was based on this code in EM 5.3.
serverclass=EM6.1
This indicates an extension tool built for EM 6.1 or later. After feedback from users of the experimental extension tool in EM 5.3, we developed a production extension tool definition for EM 6.1. This release includes many new features that aid custom tool development, such as the very powerful &EM_ACTION design.
Gerhard's superb work is based on the the EMCODETOOL class and will continue to function. Newer custom may take advantage of the EM6.1 level extension specification.
Hope that helps!