I thought about this, its ok to use what every cue or shaft you want during play but as soon as you switch to this cue or that cue to specifically jump--It's not ok, afaik. Only in tournaments where jump cues are not allowed and maybe not in 1pocket.
The logic makes sense to a degree, your going to switch to a standard maple shaft to jump and an LD shaft for english /accuracy shots or some variation but you would never use a LD shaft to help with your jump. I always thought pool would eventually mimic golf to a T--Haa get it.
you have 3 to 4 cues to cover all shots but I think it's too pricey. ATM we have jump cues, break cues, Masse cues, playing cues. It's getting close. I have seen pros switch out shafts before.
For example, you have a long draw shot, grab your 12mm carbon. You want to just hit center ball, grab your 12.9 carbon. You need to jump, grab your 13.2 stiff maple. Does the physics actually benefit you? A video for Spin Junkies maybe. My thoughts are not much but there is a balance point.
Thank you for your input.
I think it feels like it should not be an issue other than a certain house or TD's rule or determination.
My personal example would be not really anything odd. Just a stiffer shaft cue for more accurate long shots (and more than a sliver's worth of jumping), and still a standard cue/shaft/tip). Think Joss vs. Meucci.
Knowing this game, someday the OP rules may add a blurb about not changing regular cues or shafts for other than an equipment failure.
I sometimes avoid a more flexible cue when I don't play much, but might switch during a game if I need extra spin/action. Should not matter the way it is phrased now, as long as the cue or shaft isn't designed or sold as a special-purpose type like the ones you mentioned.
I agree the equipment variations are getting to be a lot like in golf. People adding/removing weight, different style tips, screw-in extensions, using vacuum tubes as extensions or slip-ons, specialty bridges, specialty chalk of course. It seems only limited by one's imagination until a rule tries to compensate.