Hi Karina Perez ;
You can use blanket purchase order with account assignment Asset. But, you have to decide how you manage good receipt requirement. Item category B limit is a special account assigment so unconsider good receipt.
If you decide to use blanket po, please look at characteristics from Purchase Order vs Framework Order
However, you have to configure ''Define Combination of Item Categories/Account Assignment Categories'' , OMG0 tcode your path.
Regards.
M.Ozgur Unal