In mt I added the folloing line:
mods.techreborn.blastFurnace.removeRecipe(techreborn:ingot:28);

And when reloading I got:
ERROR: Error executing recipe.zs: null
java.lang.NullPointerException
at techreborn.compat.minetweaker.MTBlastFurnace$Remove.apply(MTBlastFurnace.java:92)
at minetweaker.runtime.MTTweaker.apply(MTTweaker.java:70)
at minetweaker.MineTweakerAPI.apply(MineTweakerAPI.java:169)
at techreborn.compat.minetweaker.MTBlastFurnace.removeRecipe(MTBlastFurnace.java:76)
at Recipe.script(recipe.zs:177)
at ZenMain.run(recipe.zs)
at minetweaker.runtime.MTTweaker.load(MTTweaker.java:163)
at minetweaker.MineTweakerImplementationAPI.reload(MineTweakerImplementationAPI.java:656)
at minetweaker.MineTweakerImplementationAPI$1.execute(MineTweakerImplementationAPI.java:83)
at minetweaker.MineTweakerImplementationAPI$19.execute(MineTweakerImplementationAPI.java:642)
at minetweaker.mc1710.server.MCServer$MCCommand.func_71515_b(MCServer.java:124)
at net.minecraft.command.CommandHandler.func_71556_a(CommandHandler.java:94)
at net.minecraft.network.NetHandlerPlayServer.func_147361_d(NetHandlerPlayServer.java:739)
at net.minecraft.network.NetHandlerPlayServer.func_147354_a(NetHandlerPlayServer.java:718)
at net.minecraft.network.play.client.C01PacketChatMessage.func_148833_a(SourceFile:37)
at net.minecraft.network.play.client.C01PacketChatMessage.func_148833_a(SourceFile:9)
at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:212)
at net.minecraft.network.NetworkSystem.func_151269_c(NetworkSystem.java:165)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:659)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:547)
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:186)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:427)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685)