dnd 5e – Does the new Feywild Shard from TCE replace the initial spell or simply add on to it?

So Tasha’s Cauldron of Everything has an item called a Feywild Shard with the following text:

This warm crystal glints with the sunset colors of the Feywild sky and evokes whispers of emotional memory. As an action, you can attach the shard to a Tiny object (such as a weapon or a piece of jewelry) or detach it. It falls off if your attunement to it ends. You can use the shard as a spellcasting focus while you hold or wear it.

When you use a Metamagic option on a spell while you are holding or wearing the shard, you can roll on the Wild Magic Surge table in the Player’s Handbook. If the result is a spell, it is too wild to be affected by your Metamagic, and if it normally requires concentration, it doesn’t require concentration in this case; the spell lasts for its full duration.

If you don’t have the Wild Magic Sorcerous Origin, once this property is used to roll on the Wild Magic Surge table, it can’t be used again until the next dawn.

The middle part is the one that some in my group don’t agree on. I read it as you cast a spell that is being affected by metamagic. You then choose to roll on the table. If the effect rolled is then also a spell it is separate from the original spell and has the two listed added conditions. The others think that if it rolls a spell that it replaces the original spell and the original metamagic doesn’t affect it.