Below is a registry export of what seems to control the HTML editor in my system.
Maybe you can doctor it for your own use. UltraEdit-32 is what I mostly use for editing
text.
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Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Default HTML Editor]
"Description"="UltraEdit-32 Professional Text/Hex Editor"
[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Default HTML Editor\shell]
[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Default HTML Editor\shell\edit]
[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Default HTML Editor\shell\edit
\command]
@="F:\\PROGRAMS\\ULTRAE~1\\UEDIT32.EXE \"%1\""
[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Default HTML Editor\shell\edit
\ddeexec]
@="[open(\"%1\")]"
[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Default HTML Editor\shell\edit
\ddeexec\Application]
@="UEDIT32"
[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Default HTML Editor\shell\edit
\ddeexec\topic]
@="System"
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