I kept mine when I sent the forms off, on the advice of the FEO. Without your ticket you can't buy ammunition remember! My FEO picked up my old ticket when he came for the interview. I had enough ammunition to last, but he would have given me a temporary ticket if I'd needed it.
Speak to your FEO and ask him what's best for them. Remind him that you may need to buy ammunition, especially if the variation is complicated at all.
Also, without your cert, you can't take the guns out anywhere. Well, you can, but if you are stopped with them, and don't have a valid cert, then they will seize