using text properties in a buffer that is older than its file

[Drew Adams <drew.adams@oracle.com>]

Suppose some code just modifies some text properties.  This is
considered by Emacs to be a buffer modification, and if the
file has been changed externally since it was last visited in
the Emacs session, then trying to modify the text properties
prompts the user with:

  ... changed on disk; really edit the buffer?

(This is done by `ask-user-about-supersession-threat'.)

Saving, resetting, and restoring `buffer-modified-p' is not
sufficient to inhibit this user prompting.  And if the code
is called multiple times then the user gets prompted multiple
times (assuming a response that keeps the buffer unsynced).

What is a good way to inhibit this prompting?  Binding
`buffer-file-name' to nil works, but is there a better way?

Is there now (shouldn't there be?) a way to tell Emacs that
within some scope it should not consider text-property changes
to be buffer modifications - at least for purposes of
consideration by `ask-user-about-supersession-threat'?

That would be much better than binding `buffer-file-name', as
it could be done around code that might let a user modify the
buffer (text changes, not just property changes), and the user
would still get prompted for any real text change.

I'm hoping that there is already a feature for handling this
kind of use case, which I'm just unaware of.