Can I ruin my muscle repair after tummy tuck?

Thank you very much for the question.Postoperative care after a Tummy Tuck are very important to get the best results.To avoid damaging the muscle repair, you have to avoid any activity to increase the intra-abdominal pressure, that's mans, avoid efforts like carry much weight or becoming constipated.Kind regards,Dr. Emmanuel Mallol Cotes 

Sewing the muscles together in the midline of the abdomen
during a tummy tuck (also known as rectus plication) is a powerful procedure and
can be associated with dramatic improvements in body contour. The repair can act
like an internal corset, flattening the abdomen and eliminating bulges that can
be seen after pregnancy and weight loss. Excessive stress on the muscle repair
can promote its failure after the procedure. Either the stitches used to perform
the repair can break, or the stitches can tear through the tissues- both events
can affect the ultimate result. It is important to refrain from strenuous activity
and heavy lifting for 6-8 weeks after tummy tuck procedurs to decrease the chance for
failure of the muscle repair. Good luck. Best regards.

Sure but why would you?  It sounds like you are well informed as to what your surgeon did to correct your fascial defect.  Unfortunately we are made out of tissues which can stretch and give in response to pressure.  Best bet is to follow your surgeon's advise on post op lifting and exercise.  Be patient with your recovery. It will pay off in the long run.