You said drive 0 rebuilt ... so there is no need to change anything. It isn't " once a hot-spare, always a hot-spare" ... once it rebuilds, it is no longer a hot-spare, but a fully participating member of the array, meaning you no longer have a hot-spare. To replace drive 2, force it offline (or prepare to remove/replace, etc.) first ... if it doesn't start rebuilding automatically, then assign it as a hot-spare. Reconfigure is completely different.
Raid 5 setup on an R310, Drive 0 failed and removed itself from the array seemingly (so now we have a 2 drive raid 5), wasn't listed as part of it so we had to replace it and assign as a global hot spare, that built itself correct and the VD is no longer marked as "degraded", but we also have to replace drive 2 and I wanted to know the correct way to add Drive 0 back into the array not as a hot spare but as part of it?  We have OMSA and can provide screenshots.  I'm leaning towards "reconfigure array" but I've never dealt with this specific issue before
R310 Raid 5 - Lost 1/3 disks