  The outflows from neutrino-cooled black-hole (BH) accretion disks formed in
neutron-star mergers or cores of collapsing stars are expected to be
neutron-rich enough to explain a large fraction of elements created by the
rapid neutron-capture (r-) process, but their precise chemical composition
remains elusive. Here, we investigate the role of fast neutrino flavor
conversion, motivated by the findings of our post-processing analysis that
shows evidence of electron-neutrino lepton-number (ELN) crossings deep inside
the disk, hence suggesting possibly non-trivial effects due to neutrino flavor
mixing. We implement a parametric, dynamically self-consistent treatment of
fast conversion in time-dependent simulations and examine the impact on the
disk and its outflows. By activating the, otherwise inefficient, emission of
heavy-lepton neutrinos, fast conversions enhance the disk cooling rates and
reduce the absorption rates of electron-type neutrinos, causing a reduction of
the electron fraction in the disk by 0.03-0.06 and in the ejected material by
0.01-0.03. The r-process yields are enhanced by typically no more than a factor
of two, rendering the overall impact of fast conversions modest. The kilonova
is prolonged as a net result of increased lanthanide opacities and enhanced
radioactive heating rates. We observe only mild sensitivity to the disk mass,
the condition for the onset of flavor conversion, and to the considered cases
of flavor mixing. Remarkably, parametric models of flavor mixing that conserve
the lepton numbers per family result in an overall smaller impact than models
invoking three-flavor equipartition, often assumed in previous works.
