With a touch you can alter the power of a parahuman by modifying the Corona Pollentia. Doing this makes the mind of the shard and its host to slowly merge, resulting in the shard having greater control and the host mind degrading, the more you modify the connection the quicker the merge happens and the more the host power is amplified. With a touch you can return the connection to normal, but the host mind will need time to become whole again, the further the host and shard are merged the longer it will take for the host mind to recover.
When you alter the connection between host and shard you can give the host a new power that the shard could have given during the host trigger event by sacrificing parts of the existing power with the new power potency being directly proportional to the sacrifice, for example giving a pyrokinetic the capacity to slowly fly by reducing their control over their fire.