You wont have to get rid of the original system.
The previous owner of my ksp130 added a keyless entry. What it would do is if I lock the car with steel mate the factory remote wont open it.
If locked with factory remote steel mate wont open it.
Flashing lights, indicators it was too complicated I removed it later.
Then one day I suddenly missed the auto lock on brake so I installed another after marker system. Told the installer to make auto lock work only. No flashing lights, no siren no nothing. Kept remotes at home. Used Factory remote. All good.