Yes, you can lift heavy with diastasis recti as long as you can control the weight and maintain good form. If you find that your abs are bulging forward forcefully, experience any coning or doming along the midline, or feel signs of pelvic pressure such as leaking, vaginal heaviness, an urge to pee, or bladder pressure, then lower the weight or modify the exercise until you can perform it without any core or pelvic floor symptoms.