I'm of course not recommending or condoning this, but with instant release it's definitely possible to also get a higher dosage than you actually need and cut the pills up to take the lower dosage you need, and stash the rest to build up a surplus.
The extended release means you only have to remember to take the medication once a day instead of twice.
What we need is for these pills to be compounded the way they do opioids: the wax granules are arranged to attempt to keep you from getting a burst dose by crushing the pills. The same process that makes crushing work makes splitting not work. So if you make split pills still time release, no problem.
But not for saving pills. Some people are exquisitely sensitive to these medications and you need 25mg per day but it only comes in multiples of 10 up to 50. So you’d like to split a 50 and take 1/2 pill per day. Also the 40mg often costs only 30-40% more than the 20.
One thing to keep in mind that methylphenidate is contextual and metabolic related.
Hard focus work could make it work shorter, but also some have metabolism so quick that they burn through medication. That's controlled by doctors so no worries, but I know people who take IR forms every 2 hours, and for those XR forms don't work at all (as it's like 2 complete cycles with all side effects).
Vyvanse is biochemically rate-limited rather than mechanically, so it is ideal for this; there is not really an alteration to the absorption properties no matter what you do.
When I was taking ADHD stimulants I had my core dose (long release) and then a “top-up” dose (5mg instant release) every month. The guy who prescribed me initially may have been a bit of a quack (I had to leave him because my insurance dropped him) but when I switched to a super mainstream doctor she had no problem continuing it.
you can open the XR/LR capsules too, there's just a bunch of small "grains" inside, with different coatings, and thus they get digested at different rates, and basically it's like eating one instant release and one ~4 hour release capsule. (though there are fancy ones that have ~3 peaks, etc.)
you can simply measure the grains with a scale and separate some fraction.
Or so I've heard.