If ya go and look a little bit further down the Unearthed Arcana that is the source of the Lore Mastery Wizard, you'll get this little tidbit.
While the Spell Secrets feature offers increased versatility, at the table its effects can be difficult to spot
by the other players. If you’re playing a savant, take a
moment to describe how you alter your spells. Think of
a signature change your character is particularly proud
of. Be inventive, and make the game more fun for
everyone by playing up the sudden, unexpected tricks your character can employ.
For example, a fireball transformed to require a Strength save might become a sphere of burning rock that shatters and slams into its target. A charm person that requires a Constitution save might take the form of a vaporous narcotic that alters the target’s mood.
It doesn't specifically address changing damage types, but it encourages you to be creative with the descriptions, and emphasize the differences you have wrought in your spells through this feature.
Additionally, from a 'common sense' approach...a Fireball that does Ice damage should look like an ice blast, not a fire blast.
Spell Secrets should absolutely change the appearance of spells.