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You could always use reflection. Make sure to use ReflectionHelper.getPrivateValue and provide both the deobf name of the field as well as the SRG name.

It is not possible with an IRecipe, butt you can use Item#onCrafted and/or Item#onUpdate

ITT: Spoonfeed me answers or I'll get angry

100% wait. The fundamentals of the Minecraft codebase have changed quite a bit; as such, the Forge layer on top of it will need to change drastically. I'm almost certain that even those of us who have been using Forge for awhile will have to "re-learn" the 1.13 structure, as it were. So you may as well wait until then to start learning so you don't have to start all over

Mods always need to be updated to work with new versions, because they depend upon bits of the Minecraft source code, and the Minecraft source code changes with each update. It's rare to have none of Mojang's changes affect your mod. But even more than that, don't forget: before Minecraft 1.13 was the Update Aquatic, it was first the Technical Update. It used to be that 1.13 was the Technical Update, and 1.14 was the Update Aquatic. But then the two updates got merged into one, blah blah blah, and now here we are. I mention all this because the Technical Update, as its name suggested, changed a lot of the core Minecraft code, more than usual. The command system was totally rewritten, so any mods that added or used commands will break from that alone. But even worse (better?), the Flattening happened. Block and item IDs were removed. Block data values were removed. All identifiers are now strings, and all extra block data that doesn't require processing is now a block state with no backwards compatibility for numerical metadata. (I mean, to be fair, it's been 5 versions since block states were introduced, so it's about time the transitional period ended.) Which means any mod that adds, removes, or interacts with blocks or items must be updated. So unless you have a mod that does nothing with commands, blocks, or items, you're guaranteed to have to update it. And there's no promise that even if you have such a limited mod, you won't have to update, because there are many more changes under the hood than what I've mentioned (for instance, item entities now behave differently, too, so some entity code would need to change as well!).

Never gunna happen, welcome too the world of Minecraft Modding.