No. You cannot partially withdraw the money from your iWish deposit mid-way. You can withdraw money mid-way by closing your iWish. However in that case, you will earn interest at the rate corresponding to the period the iWish is held with the bank. Please note that the applicable penalty will be charged for premature closure of iWish.
If an iWish deposit is prematurely closed, then the interest on it will be earned for the period it is held with the bank minus the premature closure charges of 0.5% if original tenure is less than 1 year and 1% for more than 1 year.