A friendly neighbourhood pharmacist weighing in here. The general advice is not to exceed 4g / day. That said, there is a great trick to prevent liver damage with APAP.
Drink alcohol while you take your percs. I know that sounds counter-intuitive, so let me explain a little. How APAP is toxic to your liver is that one of its metabolism pathways is via an enzyme called CYP2E1, which leads to the toxic metabolite NAPQI (N-acetyl-p-benzoquinone imine). Ethanol is also metabolized (in a small part) by CYP2E1, and the chronic consumption of ethanol causes the upregulation of CYP2E1. Having more CYP2E1 means that more NAPQI is produced when you take APAP. The trick is though, that CYP2E1 will PREFERENTIALLY metabolize ethanol over APAP. This means that as long as you have ethanol in your blood stream you’re protected from the toxic effects of APAP.
Read more here: Paracetamol, alcohol and the liver Of course, chronic alcohol consumption is damaging to your liver in its own right, so I guess my real advice is don’t be lazy, do a CWE. Minimize the risk to your liver; you only get one.