Does this work, and if this does work can it be a config file too so i dont have to redistrubte the jar?

Or does making a resource pack with the json files work? I honestly dont know

In 7.99.17 the only way of adding new assembly recipes is to add them to a mod jar file, it doesn't have to be BuildCraft itself. Looking in the config folder sounds like a reasonable addition.

So yes it will work but please don't do this because it will be broken in a week when 7.99.18 comes out.

also what is 7.99.18 doing to assembly

I wont but your saying i could just make a empty mod with mcreator and add the files in. or does it have to be BC related

Assembly recipes will change with the MJ update (whenever that comes out), however 7.99.18 will probably scan the config folder as well.

is 7.99.18 the mj update

No, that's later. 7.99.18 is just going to be a bugfix update.

Also if you wouldnt mind me asking. Buildcraft is in beta or release but its flagged as alpha on curse so people dont break the mj api

Also it seems that the Buildcraft compat module still doesnt read assembly recipes

No, BC is still in alpha (as marked on curse) and will stay in alpha till all the features that are being reworked on are complete and the mod is feature complete compared to 1.7

The BC compat module for 1.12 does not have JEI integration to display the assembly table recipes and it will not be added till the assembly table api is rewritten in MJ update so it will be added sometime after that.

Please use the discord for random questions such as these next time: https://discord.gg/BuildCraft