If the upgrades add weight or hull is modified then there will be a degradation in speed and maneuverability. There can also be an issue with electrical power supply and back up power if the added equipment requires more power to operate.
Generally, the main power plant and back up generators are over rated as compared to the current requirement. As far as I know, German designers of power plants and generators, as a thumb rule, keep about 15% over rating on when designing their equipment on the min. side. I know for a fact that some Duetz Generators upwards of 25KVA over rated by upto 20%!