Unbolt the old one,fit the new one.Do not use a bridging battery.This could be dangerous if the cables short out or touch the bodywork.The radio code should be stored in the car electronics.Nothing will default to factory settings.

A lot of the car info is stored in the instrument cluster electronics.Your car may be early enough to need a code input.You will not know until you reconnect the battery.The radio may show "learn" on the display when switched on,in which case it will take the code info from the cluster,so no need to input any digits on radio.

You could get away with the assistance of a battery charger connected to the old battery terminals, which could be removed quickly from the battery. Then lift out the old battery replace it with the new, replace the terminals then quickly remove the charger. I used a CTEK (type) charger, and had no problems and the radio code setting was not disturbed.

You are an asset to this forum, elekie doctor, as "you know your stuff"!

I use a battery powered memory saver.

No problem at all,as long as a low current charger is used.Ctek chargers or similar are ideal for this.Don't use an old fashioned charger that you might have found in your dad's shed from the 1970,s.