I want to replace a block in a vanilla structure (ruined portal) with another block. I can see two ways of doing this, neither of which are ideal.

1. Overwrite the NBT files containing the structure variants like a data pack after loading and editing the structure in-world (or edit the NBT directly with an editor, not sure which is simpler). First of all, this is tedious, as the structure has 13 variants, and can't be done in code alone. This method is also limited, as I can only change the blocks themselves, not add a new processor, which I would prefer (e.g. to only replace the block 50% of the time). It also just seems ugly to overwrite an entire set of structures for a simple change, and it is not compatible with the addition of more variants by another mod/datapack/vanilla update.

2. Mixin to add one line of code to put a new ProcessorRule in the StructurePlaceSettings made by makeSettings in RuinedPortalPiece. Downside: mixin.

Is there a simple and flexible way of doing this that does not require a mixin? E.g. an event when a structure is placed, a way to track down the TemplaceStructurePieces and append to their StructurePlaceSettings, etc?

If there is no easier way, which method above seems more appropriate?

 

what you need to make is a StructureProcessor. look into classes that extend StructureProcessor (ctrl+H in idea ide). instances of that class replace single blocks in structures.

that part was easy. second part is squeezing one into the game. you need to find a configured feature/structure, find a list of processors and add your processor into processor list. you may need an AT or two but i don't expect you'd need mixins.