Registry files can be fun, and everyone knows how to add things to the registry via reg files.
But you can also remove entries;
Prefix the key with '-' to remove it, set the value to '-' to remove it.
[-HKEY_LOCAL_MACHINE\Software\Foo] will remove the complete key 'Foo'.
will leave the key 'Foo' and remove the value 'Bar'
Keep in mind:
The registry is a central element in windows. Messing around with it may cause unpredictabele results and the whole system may fail.
So pleas double check what you are doing to the registry!!!