This is the non-invasive version of the full Issue 2883 patch.

ly/music-functions-init.ly

 %%%% -*- Mode: Scheme -*-
 
 %%%% This file is part of LilyPond, the GNU music typesetter.
 %%%%
 %%%% Copyright (C) 2003--2012 Han-Wen Nienhuys <hanwen@xs4all.nl>
 %%%%                          Jan Nieuwenhuizen <janneke@gnu.org>
 %%%%
 %%%% LilyPond is free software: you can redistribute it and/or modify
 %%%% it under the terms of the GNU General Public License as published by
 %%%% the Free Software Foundation, either version 3 of the License, or
@@ skipping 1209 matching lines @@
 #(define-music-function (parser location tag arg) (symbol? ly:music?)
 
    (_i "Add @var{tag} to the @code{tags} property of @var{arg}.")
 
    (set!
     (ly:music-property arg 'tags)
     (cons tag
           (ly:music-property arg 'tags)))
    arg)
 
+temporary =
+#(define-music-function (parser location music)
+   (ly:music?)
+   (_i "Make any @code{\\override} in @var{music} replace an existing
+grob property value only temporarily, restoring the old value when a
+corresponding @code{\\revert} is executed.  This is achieved by
+clearing the @samp{pop-first} property normally set on
+@code{\\override}s.
+
+An @code{\\override}/@/@code{\\revert} sequence created by using
+@code{\\temporary} and @code{\\undo} on the same music containing
+overrides will cancel out perfectly or cause a@tie{}warning.
+
+Non-property-related music is ignored, warnings are generated for any
+property-changing music that isn't an @code{\\override}.")
+   (define warned #f)
+   (for-some-music
+    (lambda (m)
+      (and (or (music-is-of-type? m 'layout-instruction-event)
+               (music-is-of-type? m 'context-specification)
+               (music-is-of-type? m 'apply-context)
+               (music-is-of-type? m 'time-signature-music))
+           (case (ly:music-property m 'name)
+             ((OverrideProperty)
+              (if (ly:music-property m 'pop-first #f)
+                  (set! (ly:music-property m 'pop-first) '()))
+              (if (ly:music-property m 'once #f)
+                  (set! (ly:music-property m 'once) '()))
+              #t)
+             ((ContextSpeccedMusic)
+              #f)
+             (else
+              (if (not warned)
+                  (begin
+                    (ly:input-warning location (_ "Cannot make ~a revertible")
+                                      (ly:music-property m 'name))
+                    (set! warned #t)))
+              #t))))
+    music)
+   music)
+
 time =
 #(define-music-function (parser location beat-structure fraction)
    ((number-list? '()) fraction?)
    (_i "Set @var{fraction} as time signature, with optional
 number list @var{beat-structure} before it.")
   (make-music 'TimeSignatureMusic
               'numerator (car fraction)
               'denominator (cdr fraction)
               'beat-structure beat-structure))
 
@@ skipping 64 matching lines @@
                     value
                     (ly:music-property music 'tweaks)))
        (ly:input-warning location (_ "cannot find property type-check for ~a") prop))
    music)
 
 undo =
 #(define-music-function (parser location music)
    (ly:music?)
    (_i "Convert @code{\\override} and @code{\\set} in @var{music} to
 @code{\\revert} and @code{\\unset}, respectively.  Any reverts and
-unsets already in @var{music} are ignored and not converted.")
+unsets already in @var{music} cause a warning.  Non-property-related music is ignored.")
+   (define warned #f)
    (let loop
        ((music music))
      (let
          ((lst
            (fold-some-music
             (lambda (m) (or (music-is-of-type? m 'layout-instruction-event)
-                            (music-is-of-type? m 'context-specification)))
+                            (music-is-of-type? m 'context-specification)
+                            (music-is-of-type? m 'apply-context)
+                            (music-is-of-type? m 'time-signature-music)))
             (lambda (m overrides)
               (case (ly:music-property m 'name)
                 ((OverrideProperty)
                  (cons
                   (make-music 'RevertProperty
                               'symbol (ly:music-property m 'symbol)
                               'grob-property-path
                               (cond
                                ((ly:music-property m 'grob-property #f) => list)
                                (else
                                 (ly:music-property m 'grob-property-path))))
                   overrides))
                 ((PropertySet)
                  (cons
                   (make-music 'PropertyUnset
                               'symbol (ly:music-property m 'symbol))
                   overrides))
                 ((ContextSpeccedMusic)
                  (cons
                   (make-music 'ContextSpeccedMusic
                               'element (loop (ly:music-property m 'element))
                               'context-type (ly:music-property m 'context-type))
                   overrides))
-                (else overrides)))
+                (else
+                 (if (not warned)
+                     (begin
+                       (ly:input-warning location (_ "Cannot revert ~a")
+                                         (ly:music-property m 'name))
+                       (set! warned #t)))
+                 overrides)))
             '()
             music)))
        (cond
         ((null? lst) (make-music 'Music))
         ((null? (cdr lst)) (car lst))
         (else (make-sequential-music lst))))))
 
 unfoldRepeats =
 #(define-music-function (parser location music) (ly:music?)
    (_i "Force any @code{\\repeat volta}, @code{\\repeat tremolo} or
 @code{\\repeat percent} commands in @var{music} to be interpreted
 as @code{\\repeat unfold}.")
    (unfold-repeats music))
 
 void =
 #(define-void-function (parser location arg) (scheme?)
    (_i "Accept a scheme argument, return a void expression.
 Use this if you want to have a scheme expression evaluated
 because of its side-effects, but its value ignored."))
 
 withMusicProperty =
 #(define-music-function (parser location sym val music)
    (symbol? scheme? ly:music?)
    (_i "Set @var{sym} to @var{val} in @var{music}.")
 
    (set! (ly:music-property music sym) val)
    music)