"The Household sector has devoted much of this windfall gain in income towards a greater hunger for imports"

When referring to a L-J (Leakages-Injections) graph will this be a change in EXOGENOUS IMPORTS or Marginal Propensity to Import?

With your one-sentence description of issue could easily be taken out of context. That said, I believe the answer is "change in exogenous imports"

When interpreting the statement in the context of a L-J graph, it suggests a change in exogenous imports, meaning an increase in imports that is unrelated to changes in income or other factors.