No adding the extra canister for di resin is fine but it means that you need to change the plumbing so that the water goes through all 3 canisters on the filter (assuming the 3rd one is a sediment or carbon) before it feeds into the membrane. Then the permeate (good) water from the membrane should go over to your extra di canister then to your storage container. The condensate (waste) side of the membrane should go through a restrictor, and then you can use the one with a flush valve or have a tee or wye with a ball valve that bypasses the restrictor to flush the membrane periodically.
Also your tds probe should be moved to after the di canister that was added.