Evolve/Increase unit rarity/Add star in name

[VivoPresto]

Is it possible to evolve unit from:
People's Dagger (UC) to *People's Dagger* (UC)
or
Harpy (UC) to *Harpy* (R)?

How to do it?
Does unit must be level 1 or max level?
Does unit must be promoted or not promoted before?

[Obamallama]

Nah they are different units but the star versions are just better. It ranges from C to UC all the way to R to SR

I'm pretty sure all UR have SR equivalents but different names.