Q. If Electron affinity or Eg is changed, how should band
offset ration is set?
Do you have any reference?

Answer:

If I have two materials, say 1 and 2, and material 1 has a lower bandgap than material 2. Below I will assume the type I heterointerface and will no mention the offset sign, but the system can handle also type II heterostructure, like Zno/GaN one.

Then the conduction band offset is calculated as

dEc = ElectronAffinity_1 - ElectronAffinity_2
dEv = (ElectronAffinity_2 + EnergyGap_2) - (ElectronAffinity_1 + EnergyGap_1) = EnergyGap_2 - EnergyGap_1 - dEc

Next, we want to set up a fixed band offset ratio, say dEc/dEv = 7/3 = t.

From above, we can rule out the dEc value, dEc = dEg * ( t / (1+t) ).

Next, we want the band offset is constant for the whole composition range of the alloy of Material 1 and Material 2. Then we need just set the electron affinity bowing parameter
as

bowing (ElectronAffinity) = - ( t / (1+t) ) * bowing(EnergyGap)

To conclude, the user need just understand how the band offsets are calculated, and modify the electron affinity in order to get the desired band offsets.