Don't understand your question entirely but subentro means 'takeover'/'replacement'/in some contexts 'arise'

Surrogacy (but note the Surrogate's Court in the US of A: 2nd example sentence), subrogation (*to* a party *in* the latter's rights and, despite g/hits, not *to* the latter's rights), substitution and assignment or succession-in title -> Garzanti: replacement, succession and taking over doesn't make much sense in the context, rather a more literal rendering seems to be called(-)for.

La procedura di ***subentro*** dei Comuni in Anagrafe Nazionale della Popolazione Residente : The procedure for sub-inputting or 'subbing' (switching the particulars of the) Borough Councils / Local Authorities into National Resident Population Registers (UK: Electoral Registers or Voting Lists) i.e. such authorities are deemed on par with human residents.