Hi, i dont know anything about minecraft modding, but really want to combine mods into a modpack. I really wanna play fycraft mod wich adds hoppers to beta. It's not really compatible with other mods, is it possible to extract the hopper out of the class-files from the mod and make a custom mod. And if so how?
You can use Mod Coder Pack to decompile the modded jar (if you are referring to this mod it says it is a jar mod, so you add it to the Beta 1.7.3 jar, then place the jar in the folder indicated by MCP. I've done this to decompile an Optifine-modded jar (1.6.4) and modify it without any issues other than the installer/Forge tweaker files needing to be deleted and an incorrectly decompiled line in RenderBlocks (MCP may say something about "hunk failed" and save a file containing the problematic code):
One potential major issue is that MCP may expect the old .minecraft directory structure (with a bin folder and all; the instructions tell you to copy files from it, while newer versions, such as 1.6.4, do it automatically, either way, it doesn't exist anymore, at least not under the vanilla launcher, which is all that I've used so I can't say anything about other launchers). I've also seen people have trouble running ModLoader mods for the same reason.
Of course, you'll also need modding knowledge; the hopper class is probably easy to find (something like "BlockHopper" and "TileEntityHopper", as MCP named them in 1.6.4) but you'll need to modify all the necessary vanilla code and this may be where the compatibility issues stem from (e.g. only one mod can modify the "Block", "TileEntity", "Item", etc classes, which must be modified to add in references to new things, so you may have to alter the classes from other mods to include them; one way would be to decompile the modded jar without Fycraft, then add in the hopper code, after which MCP should reobfuscate the modified/new classes (if any errors occur after the first decompilation run "updateMD5" after fixing them but before adding the hopper code).