Hi toby320, here is your answer,
You set the applicable CAT I minima on the MDA field.
You are allowed to perform an autoland (yes autopilots remain engaged in LOC GS modes even below MDA-50) in CAT I conditions or better and at least CAT II landing capability displayed in the FMA. If autoland light on take over manually (in CAT I conditions you most probably wil have visual references) or go around.
Take into acount LSA might not be protected and remember your CAT I minima is your decision altitude which means you have to go around if no visual references by this altitude.
By the way you are allowed to perform autoland under these conditions even in CAT I only installations.
Regards.
Edit: Wizzaird was a bit faster than me.