I see how you can add the additional AJ lines for Box 20 but I see no way to change the text provided from anything other than "Excess Business Loss Limitation". Going into forms at this point only shows one AJ line with the same text followed by "*" which goes to a note underneath stating "Not provided for in program. Manually enter on appropriate tax form." So giving @PatriciaV suggestion a go with ZZ instead of AJ.
My AJ entries on the K-1 are:
Aggregate Business Activity Gain (Loss) of Dispo. of Property
Aggregate Business Activity Gross Income
Aggregate Business Activity Total Deductions
