I don’t think it allows you to borrow more than the 50% right now, it did at first, but I think they fixed it,
If you did book with more than 50% of borrowed points, it will get caught and will be canceled
Now, if the trip you modified was booked prior to April 24th with more than 50% of the borrowed points, you are okay.
Go to your dashboard and look at the number of points you have borrowed...if you are over 50% and the modification you did the other day used some newly borrowed, then you should call because it will get adjusted at some point.