Marinating chicken for an extended period can certainly intensify the flavors, but you're right to be mindful about the potential for the texture to change. Typically, chicken can safely marinate in the refrigerator for two days.
Salt and vinegar in your marinade do act as tenderizers and could start to alter the texture of the chicken over time. If it's a high-acidity marinade (which might be the case with a Nandos-style marinade because of vinegar), leaving the chicken in it for more than 24 hours could potentially cause the meat to become a bit mushy. However, this largely depends on the exact composition of your marinade and the ratio of acid to other ingredients.
Always remember to check the chicken before cooking. If it smells off or has a slimy texture, it's better to err on the side of caution and discard it.