In this work, we revise and update model-independent constraints from Big Bang Nucleosynthesis on MeV-scale particles $\phi$ which decay into photons and/or electron-positron pairs. We use the latest determinations of primordial abundances and extend the analysis from 1808.09324 by including all spin-statistical factors as well as inverse decays, significantly strengthening the resulting bounds in particular for small masses. For a very suppressed initial abundance of $\phi$, these effects become ever more important and we find that even a pure 'freeze-in' abundance can be significantly constrained. Besides, we also present our new public code ACROPOLIS, which numerically solves the reaction network necessary to evaluate the effect of photodisintegration on the final light element abundances. Including the process of photodisintegration into the numerical analysis is e.g. especially important for the scenarios discussed in this work, as it can significantly change the abundances after standard BBN due to late-time high-energy injections, thus leading to more stringent limits. Finally, in an independent part, we also present precision calculations of the annihilation cross-section required to match the observed DM abundance in secluded dark sectors. We demonstrate that the difference to the canonical value is generally sizeable, and can reach orders of magnitude.
