Thanks for your enquiry.
The risk manager checks the trader's exposure after the new trade has been opened and acts then to accommodate the total exposure to the 10% target VaR.
It will then adjust the DARWIN's total exposure, either partially closing some of the previously opened positions and/or adjusting the size of the most recent trade.
Please note that the DARWIN does always replicate trades (i.e. if the trader goes long the EURUSD, it cannot happen that the DARWIN does not go long the EURUSD because of the risk, it will do so but adjusting the total exposure to the DARWIN's target risk).
I hope this helps!