Abilities » Almighty Evolution
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.
Source: Lost Thunder FAQ (2018-10-20), TPCi Rules Team (2018-11-01)
Abilities » Almighty Evolution
If I have placed a Stage 1 Pokemon onto Ditto {*}, can I later evolve that into the corresponding Stage 2 Pokemon?
Yes, you can!
Source: Lost Thunder FAQ (2018-10-20), TPCi Rules Team (2018-11-01)