Well, when the AoS miniatures dropped and one was called a Lord Relictor, I just had to have one to put into my 40K Relictors Space Marine Battle Company.  So far I have done a lower leg and a whole leg swap to make it 40K and Terminator-esque, the model is already Terminator sized so it was making the jump from AoS to 40K using the distinctive Terminator leg greaves. I have also added a power haft to the Thunderhammer, a simple cut and shunt of the original bits.
The banner can either be just a reliquary befitting the Lord of the Relictors or the Banner of the Emperor Ascendant for gaming purposes if he is used as a Chapter Master, or maybe with the skull helm, I did think a Chaplain, but I already have a Terminator Chaplain so the Chapter Master won out. I've swapped a few trinkets for a Termie Cross and an Imperial Aquila, next up is the fiddly fitting a Crux Terminus to the Shoulder Pauldron and adding a few skulls in place of Sigmar hammers. And then maybe a Storm Shield to make him more survivable? Perhaps The Shield Eternal? The Thunder Hammer replaces his standard issue StormBolter. The Banner or Shield replaces the standard Power Sword.