I haven't played with the BPK, but most such solutions use some kind of ItemID or part number to link a LineItems table to a Products table where you store unit prices, names and other data. Usually, your product value lists are drawn from this same table.
There are several conditional value list approaches you might try--the details depend on your table structure and how you want to control which items are shown as "in" or "out" of season. You might be able to label each product with a return separated list of "seasons" and use a calculation field in your invoice table that computes the current season from the invoice date. You could then use these two fields in a relationship for a conditional value list and/or a portal to the products table.
Note: a return separated list can be created and maintained with a checkbox formatted value list. A relationship based on such a list matches values to any one of the listed values so a product with the listed values of Spring and Summer will be in season for both Spring and Summer seasons.