I doubt there is a reduction law and again the Dr is lying to save his own ass. We can't discuss that here though as it's legal discussion and against the rules.
As others said opana sucks orally and only the old ER ones had any use nasally. The IRs are good IV giving long term relief without any feindish IV rush especially the Roxanne brand genetics, but I don't recommend switching to IV. Tell your Dr that you want the morphine as it was more efficient and got through between appointments. You have very real legitimate pain and to take you off the medication while probably not illegal is beyond immoral and against the better judgement of your health care needs, which should be their only concern not whether or not the doctor should worry about the amounts your scripted coming into question as there should be acceptable answers to those questions.
In the meantime try poppy seed tea I'm sincerely nuts about a brand I just picked up, which is a lot better than the red Baron easy to find at a whole chain of stores that is still worthwhile to use in lbs rather than 1/4 that amount with the first brand. Trust me it will help a lot to make poppy seed tea. You throw them in something like a 2 liter or water bottle and shake them with lukewarm water and the cap shut. Then drain the tea by screwing the lid open just a bit, but not enough to come off and flip the bottle upsidedown and squeeze to get all the water out while holding the cap so it doesn't open and let the seeds out. You should probably filter truth a coffee filter too, but is not necessary. You want clean unwashed, untreated, and organic seeds that at higher potencies need a cup of seeds for a good batch while a bad brand need near a lb of seeds.
Keep us updated and I wish you the best. Kratom is also another option, but I think poppy seed tea would work best for you especially as morphine is the best for you