Can you evolve Ditto 
into a Stage 1 Pokemon and then on a later turn place a new, different Stage 1 Pokemon onto it?
No, not unless you have devolved Ditto somehow during a previous turn.
Almighty Evolution
Ditto
- Type
- POKEMON
- HP
- 40
- Energy Type
- Stage
- BASIC
- Retreat Cost
- Weakness
x2- Rarity
- RARE PRISM STAR
- Illustrator
- kirisAki
- Set
- Lost Thunder (LOT)
- Number
- 154/214
Abilities
Almighty Evolution
Once during your turn (before your attack), you may put any Stage 1 card from your hand onto this Pokémon to evolve it. You can’t use this Ability during your first turn or the turn this Pokémon was put into play.
Rulings (2)
If I have placed a Stage 1 Pokemon onto Ditto , can I later evolve that into the corresponding Stage 2 Pokemon?
Yes, you can!
Almighty Evolution