  We present results of systematic calculations of the
isospin-symmetry-breaking corrections to the superallowed I=$0+,T=1 -->
I=0+,T=1 beta-decays, based on the self-consistent isospin- and
angular-momentum-projected nuclear density functional theory (DFT). We discuss
theoretical uncertainties of the formalism related to the basis truncation,
parametrization of the underlying energy density functional, and ambiguities
related to determination of Slater determinants in odd-odd nuclei. A
generalization of the double-projected DFT model towards a no core
shell-model-like configuration-mixing approach is formulated and implemented.
We also discuss new opportunities in charge-symmetry- and
charge-independence-breaking studies offered by the newly developed DFT
formalism involving proton-neutron mixing in the particle-hole channel.
