I am using BlendAPPs for our QC data results, I have a field for LOT/Batch number that they say can't be made to be mandatory. Is there something I can script to make the field mandatory?

If it's on a Suitelet, then you would need to modify the Suitelet itself to handle the validation or inject some client side code to do so. It is definitely possible, but generally not recommended because future BlendAPPs updates will likely override the updates made.