Hello! I am trying to make automatic slag to ores subfactory and i noticed that i can't set desired recipe in assembler by signal (there is no proper recipe signals for efficient slag processing, iron-rich, copper-rich or uranium rich).

I had no idea that was a thing...

Unless you know better, it looks like you can't set an assembler's recipe directly, you can only choose the product you want it to make. For example, choosing iron ore will set the recipe for slag. I've seen some articles regarding multiple output signals and the assembler reading only the "strongest" signal.
I don't believe there is anything I can set in the recipe to change this behaviour.

Recipe signals can be specified for different recipes. Now if i send iron ore signal to an assembler and choose to set recipe - it will start doing basic slag processing (not iron-rich for example). Other mods can specify different recipe signals for diferent recipes to address this issue. For example https://mods.factorio.com/mod/scrap-industry.

OIC, got it.
Will be fixed in the next update.

It works, ty!