The effects are dose-dependent, and peripheral conversion is typically a concern for parkinson's patients using 15-20x the dose of l-dopa found in a serving of inhibit-P. You can use EGCG if you choose, but again, dose-dependency becomes an issue. If you want to achieve the effects of clinical decarboxylase inhibitors administered to PD patients, you would need about 40 caps of your typical highly-concentrated green tea extract. However, 5g of EGCG is a good starting point for mild decarboxylation if you can afford that.
At the end of the day, I wouldn't worry about adding or subtracting anything from Inhibit-P. If prolactin control is your concern, it will do you well.