It's not really possible to extract the drug from the extended release components without knowing exactly what chemicals they used and doing some chemistry to dissolve the components you don't want in a chemical that only disolved that chemical and not the drug.
As for reducing dosage, I do that with lots of drugs for rationing purposes either due to shortages, insurance delays, or financial issues. If it's a capsule, you usually can pull the two sides apart and take a portion of the drug inside. Some have multiple different components inside, but usually they are randomized enough during shipping that you'll get a fairly even distribution of the components.
If they are solid tablets, it depends. Some you can cut with a pill cutter, but some will cause issues because they are designed to be digested more slowly and taking it cut can cause unpredictable release timing.
Disclaimer: not a doctor or pharmacist, just have had to ration meds a lot due to the crappy healthcare system in the US.