Probably better if you can gain access to individual battery cells to use smaller lower voltage power supplies/chargers for this, or at least split up the pack into more manageable parts (safer too). The more cells you have in series the more chances there will be imbalances, which will be a detriment to attempts to "refresh" the NiMH pack. It could even be damaging if you plan on deep discharging it as part of the refresh process as weaker cells could go negative and that is not good for them.