You also need to consider whether cis or trans isomers are produced.
[Co(NH3)4CO3]+ is necessarily cis, as the carbonate group acts as a chelator, it binds to two adjacent positions. So simple replacement of carbonate by H2O or Cl- would give the cis isomer (H2O or Cl- in adjacent positions).
However the trans isomers, with H2O or Cl- in opposite positions, are more thermodynamically stable, and will be favoured if the solutions are hot, giving the activation energy to allow the conversion.
If nitrite is added we would expect the cis or trans dinitro complexes [Co(NH3)4(NO2)2]+ to form.