[次第「じだい」]だ => It depends on A N2
Based, Focused, Depending on
[次第「じだい」]では => Depending on A, B may change N2
Based, Focused, Depending on
[代「か」]わり => Not A, but B, B in place of A, Instead of A, B; In exchange for A, B N3
Comparison, Exchange