Can i request a formal child custody agreement while separated?

Yes you can, and you would be wise to do so.  Courts are in favor of parties having custody agreements in place during separations, because having a formal agreement is usually in the best interests of the children and can settle potential issues such as the schedules of the parents and the children, and any disagreements the parties may have about the rearing of the children.  The best way to plan for custody of your child is to come to an agreement with your spouse in a written marital separation agreement. This agreement is like a contract that includes provisions for custodial rights and a visitation schedule.  However, some states do not allow parents to arrange for child custody in the agreement, instead requiring the parties to use a parenting plan agreement, which is separate from the marital separation agreement.   Some states require the parties to engage in mediation to create a child custody arrangement.  You would be well-advised to consult with an attorney experienced in divorce and children’s issues about the laws governing custody in your state.