V asks if can take child on vacation for longer than the parenting plan says if other parent agrees. Asks if a law applies.
Since I am not specifically knowledgeable about STATE’s laws, I can’t say if there is any specific law that would apply to the situation you are describing. In general, if one parent doesn’t follow the parenting plan, the other might accuse that parent of violating the order and take the parent back to court (and this is the reason that a parent may first file in court to modify a parenting plan). However, it is common that many parents will agree upon changes to their own plan without going to court first. Especially for minor changes, if the parents agree, most judges would not want the court to be burdened with motions to amend an order to reflect the change.
One issue to consider, however, is that if parents agree on a change, they may want to memorialize the change in a specific way that cannot be misinterpreted - and that proves that the change was agreed upon by both parties. For example, one parent may write up the agreed-upon change and then each signs it in front of a notary - or, at least the parent who is agreeing to the change would have his/her signature notarized to prevent that parent from accusing the other of forging his/her signature.
Often it depends on how amicable or not amicable the relationship is between the parents when deciding how much a parent needs to try to prepare for a later accusation of violating the order.
Again, as I said, I can’t speak to how this situation is commonly handled in your county or state and whether or not judges frown upon parents changing their own plan informally or whether it’s expected to somehow register that change with the court. You may want to try to touch base with an attorney who deals with custody issues to be sure. Here is a link for lawyers, some of which are free or low-cost - and also a link to the Bar Association which usually offers brief consultations with a private attorney for a minimal cost: LINK