No, it isn’t. It is, in fact, regular agronomical practice for tobacco growers. But once you snap the flower bud off, the plant will begin to develop suckers like crazy (in hopes to form a new flower head) and the leaves on those suckers will be few and small. Of course, you can let the plant develop as it wants, and still harvest leaves AFTER they have naturally turn yellow on the plant. Leaves will be less potent in terms of nicotine but still have the typical “wet dog smell” before kilning. If you can’t transplant in a garden, let them do their thing, enjoy the bumblebees buzzing around the yellow flowers (curiously, N. tabacum flowers attract honeybees, N. rustica flowers attract bumblebees, at least where I live), harvest, cure and kiln the leaves. It will be very instructive for your next year grow, and you’ll end up with more tobacco than you started with. Some well developed rustica strains are far more productive than traditional First Nations strains: if you are interested in productivity rather than tradition, I suggest to grow GC1 rustica next year.
@skychaser has seeds of it (and many more).
pier
Edit: the most productive strain I know of is Bakun Black (110 grams per plant on average), but I’ve never been able to put my hands on it… YET