I think your key will
ONLY work if you disconnect and reconnect wiring as it was
before the keyless install!
Otherwise you can leave it in the ignition for when you need it it - I do but mine is mounted in an 3" stub of a broken EZ-Boy recliner handle. Makes it easy to insert and retrieve key in the small gap available.
I have a spare fob from DEcosse but admit that after a year or two it still sits un-coded but I do take it with me and will con HansO into setting the frequency for me at the RAT rally in May. DEcosse has provided the instructions and it is simple but I am hopeless.