No, this is currently not possible today to give a user this granular of rights/control
OK, I have fudged a workaround.
I created an excel spreadsheet and saved it as a .htm page in inetpub\solarwinds\systemreference.
I then created a custom HTML resource, and planted an iFrame that references the spreadsheet.
I have shared the \systemreference folder, and allowed the user rights to that one folder only.
Updates appear in Orion straight after the user saves the spreadsheet.
It's not ideal, and it doesn't solve the general problem of allowing a user to edit a single page, but it has worked very well for my specific need.
Here's how I did my iFrame:
<iframe src="c:\inetpub\solarwinds\systemreference\systemreference.htm" width="800" height="600"
frameborder="1" scrolling="auto" name="systemreference">
TEXT FOR NON-COMPATIBLE BROWSERS HERE</iframe>