"If you concentrate on this spell for the full duration, the transformation becomes permanent."
"If you turn a creature into another kind of creature, the new form can be any kind you choose whose challenge rating is equal to or less than the target’s (or its level, if the target doesn’t have a challenge rating)."
By the spell's description, the only way you can change a character into a lich that way would be to transform a level 18 character into a demilich (CR 18) since a vanilla lich has a CR of 21. However, since the spell presumably wouldn't create a phylactery, the new demilich would never be able to assume its "true form".