Ultimately yes, the changes in design and when everything is done even the results of the trial will have to be recorded on ClinicalTrials.gov!
To my understanding, however, there's quite a bit todo before such a change can be made. Besides formulating an updated so called statistical analysis plan they'll have to get some new ethics board approval for the higher number of patients to be enrolled and possibly more.
Given the above (and more) formal activities that have to be implemented, IMHO it's quite normal that the entry on ClinicalTrials.gov doesn't reflect a change yet. Still I am not completely certain if such an update is mandated within 30 calendar days or only within the yearly update cycle, so I had to ask, see here
I wouldn't care so much on the entry in the trials registry, but rather communication with the FDA and when they formally have made the design change. It may seem irrelevant to us, but they are in the situation of seeing more and more of the results which in turn might introduce a bias.