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)

Relevant cards

Note: All applicable cards may not be listed below.
SM8_154