Can I replace a hidden card with another hidden card directly, since only one hidden card is allowed per battlefield?

Ruling: You cannot directly replace a hidden card with another hidden card. There is no rule allowing that.

Sequence:

• You must first play the currently hidden card (if legal to do so)
• Then you can hide a new card in its place

Nuances:

• The hidden card must be legally playable (valid target, not hidden this turn) to use this workaround
• This effectively achieves the same result as direct replacement but requires the intermediate step