Is there a way with SaveAsDialog (or another control) where I can set the InitialDirectory but not allow the user to change it?
It is a location they will have previously configured, but at this point I only want them to select or enter a filename
I think you need to roll your own.
yes… I believe you misunderstood 
I misread it (my two young kids have appeared at my feet in my office!) - I reread it, deleted the message, and you had responded to it in the meantime. Sorry for the white noise 
Then don’t present the user a “SaveAsDialog” at all. If you just want a file name, present a small modal window and get the file name.
I want them to be able to navigate thru subfolders of the supplied INITIALDIRECTORY, and enter or select a file… guess I will have to “roll my own”
Different suggestion: if the users selects a file outside the defined initial directory and hits OK, display an error message and reopen the save as dialog…
On Cocoa, you might be able to trap the event when the user changes the directory, then reset it - see