It will work beautifully, actually, What would be the reason for getting off of the heroin? Using a taper of morphine would be simplest for the reasons I outline below. If you need to maintain with morphine over a long period of that is also easier to do. I would also point out that dihydrocodeine, especially extended-release, can also be the basis of a less-complicated maintenance protocol as well. It also would seem to make a faster taper work better as well.
I am on a rotation of strong narcotic analgesics for severe chronic pain, and my experience is with being converted straight across from PO and SC/IM, IV on occasion Vilan (nicomorphine hydrochloride, 3,6-dinicotinoylmorphine) to morphine and the results were minimal side effects, especially with the route of administration. Only intravenously could I tell a difference, and that was the pins & needles, flushing, and a feeling of heat on the face. The difference was caused by the distribution and metabolism of the active metabolite, which in both cases is morphine. Then switching from hydromorphone to nicomorphine had differences Going from morphine to nicomorphine had slightly different effects also.
Having been treated medically with those medications as well as, quite some time ago medicinal diamorphine and Paralaudin (diacetyldihydromorphine hydrochloride) and experimentally with pharmaceutical/reagent grade dibenzoylmorphine and acetylmorphone and also 3-MAM and 6-MAM, I can assert that the relative amount of histamine release on administration can be quite a bit less than morphine, with the drugs in question being in the following descending order: dihydrocodeine, morphine, dihydromorphine, diacetylmorphine, hydromorphone.
So, then heroin (3,6-diacetylmorphine) does indeed have the desired effect. If you are able to have an uninterrupted supply of morphine, it will actually obviate the blow altogether as the differences betwixt heroin, which is 3,6-diacetylmorphine, are what could be called largely administrative. The body turns heroin into morphine in such a way as to make heroin more potent by weight than morphine, and causes heroin to have a stronger bang and rush, the latter having less pins & needles to it. This histamine release with morphine, the lesser nausea and emesis caused by heroin, and heroin being much more water soluble than morphine are the reasons that heroin, also called diamorphine, are used clinically as an alternative to morphine. Morphine is considered to be the benchmark for measuring narcotic analgesics, yet there are the above and other reasons that both, and usually also hydromorphone, and less commonly dihydromorphine, are used alongside each other to allow the maximal amount of flexibility in all cases.
The body begins breaking down heroin into 6-monacetymorphine and morphine within seconds and it is the morphine, and its metabolites which do the narcotising -- the two acetyl groups attached at positions 3 and 6 on the morphine carbon skeleton help the morphine across the blood-brain barrier more quickly and in larger absolute quantity . . .
Morphine hydrochloride in the form of Vendal, MST Continus and the like are used in an increasing number of countries as an alternative to methadone for maintenance and detoxification. This protocol is done also with dihydrocodeine and hydromorphone as well -- and of course, just plain pharmaceutical heroin