I want to choose different playback frame rate without affecting the project frame rate.
Looking for this kind of behavior:
On the UI click a slowdown rate on the fly 50% 25% 12% as buttons perhaps next to the playback controls. Make it slow down only when you click to prevent that you don’t mess up the project’s frame rate or manipulate to stretch keyframes.
How could this be done without either stretching the keyframes (scaling them on the Y axis) or changing the project frame rate? It would be simple to have an add-on that could change the playback speed of an individual animation by scaling the keyframes, but I’m not aware of any way to change the speed of a keyframed animation without changing the keyframes.
I’m wondering what your ideas are here. If you can think of a way to do this that has escaped me, I can make it into an add-on for you 
that existed in softimage,
so you could check the lypsync very nice because in addition the audio was played slowed down,
the animation timing was not changed,
it was just the playback speed that was slowed down.
No.
That setting is to adjust the frame rate of the project and render.
I want a momentary slow down that uses a fraction of the project’s frame rate.
Press a key or button it will play slower, unpress it will resume to the normal project’s fps.
Yes but for Blender please.
I think what @walt1 is saying echoes what I said in the first reply: how is this done without affecting keyframes or project frame rate? Blender doesn’t have a way to set temporary frame rates, at least that I’m aware of. Again, if you are aware of any way this can be done, let me know and I’ll code it for you
I just want a temporary frame rate speed. When you press a button it changes the project’s frame rate temporarily.
Use a value in a dialog box the user can choose the temporary slowed down frame rate.
Press the key, frame rate slows down to the user defined value.
Release the key, frame rate returns to the project settings.
If you can do that I’d be very grateful.
I’m sorry, I think the best I can offer is a panel to easily change the project framerate- with options for +25%, -25%, etc, and a Reset button to take it back to what it was before any tweaks. There just isn’t a way to do what you’re looking for currently available in Blender, without re-writing the source code
How about something visual as an option instead.
If I see a readout of the framerate in a box in the 3D viewport, a framerate indicator background goes red when it’s not the default speed and transparent background when it’s at the default. And percentage selector in the 3D viewport all in one.
That could be helpful.
do you want to check animations in slowed down speed
or what do you need it for,
the possibility via button-pulldownmenue would be fine for me too 
I’ll look into that and see what I can figure out
Exactly I want to check my animation.
