I have a question about visitation. If i start getting my daughter extra days consistently for weeks. Can i go back and have those permanently.

Parents can agree to extra visitation. Visitation is determined in the best interests of the child.  The court decree provides a baseline of visitation in the child's best interests in case parents cannot agree. Parents are encouraged to work together to modify visitation as they deem necessary.  Modification of a decree concerning visitation requires a substantial change in circumstances.  Getting extra days for weeks would not normally rise to the statutory requirements for a modification.  Getting extra days for years and then being cut back, might meet the requirements.  I recommend contacting a local attorney to discuss the situation.  However, if the other parent is voluntarily granting extra visitation, why go back to court prior to being denied those days in the future?