If you load up the registry editor and expand HKEY_CLASSES_ROOT, then go to .FILEEXTENSION and create a key called ShellNew. Inside that, create a new string key called NullFile with no value.
For example, if I wanted to create a new entry for a blank .BOB object I would create:
[HKEY_CLASSES_ROOT\.wil\ShellNew]
NullFile = ""
If the file extension such as .BOB does not exist, I would first create a file with that extension and double click it. Open it with the program of my choice as this would then create the other needed registry keys and make your job easier.
If you want to add a file as a template for the new item, use:
[HKEY_CLASSES_ROOT\.html\ShellNew]
"FileName"="html.html"
Then place the file (html.html) in C:\Windows\ShellNew
You can use the same logic to remove items that already exist. Hope that helps