I'm not aware of any "new" guidelines with regard to this. I believe that the present version of the regulations in CFR 1.72(p)-1 was established in 2004.
See section 72(p)(2)(A): https://www.law.cornell.edu/uscode/text/26/72
and CFR 1.72(p)-1 Q&A-20: https://www.law.cornell.edu/cfr/text/26/1.72(p)-1
I think that the highest outstanding loan balance in the past year only comes into play if the balance to your credit is not the limiting factor. Your new loan in this case would simply be limited to 50% of the balance to your credit, giving you a maximum new loan amount of $23,950.
Even if you were instead refinancing an existing loan that had a highest outstanding loan balance of $8,700 in the past year, I still don't think that the total of the new loan plus the outstanding balance of the old loan not exceeding $50,000 - $8,700 = $41,300 would come into plan since the account balance to your credit is not high enough. Your refinance would simply not be permitted to bring your outstanding balance to more than $23,950. Also, your repayment terms would need to be such that your repayments still pay off the remaining portion of the original loan amount within the originally required timeframe.
Your plan administrator is the one responsible for enforcing this, so ask them.
