An ability that turns a land into a creature also sets that creature's power and toughness. If the land was already a creature, this will overwrite the previous effect that set its power and toughness. Effects that modify its power or toughness, such as the effects of Disfigure or Glorious Anthem, will continue to apply, no matter when they started to take effect. The same is true for counters that change its power or toughness (such as +1/+1 counters) and effects that switch its power and toughness.