Idaho state law doesn't limit the number of times (or how often) you can petition the courts for child custody modification. The only requirement is that there be a substantial and material change in circumstances since your last order, which now renders the old provision(s) unworkable. Some examples of this include: parental relocations, starting school, abuse/neglect, and changes in work schedules. Under the new family law rules, you must articulate these changes in your initial complaint (upon pain of dismissal and/or attorney fees).
Of course, this is not an inherently clear standard. Most parents wonder if their "changes" are sufficient. This is why it is important to consult an attorney prior to filing your case. We can help you research the laws, look for analogous case law/situations, and make a reasoned decision based upon existing standards.