Well, I recently wanted to change some thing on a mod that is a .esm file and wanted to change some stats, so I wanted to save it and it only saved it as a .esp, but I do not want to create a new plug-in, I want to change the current stats in the mod that is a .esm. Geck wiki says that I cant save Master files, is that true? If so then my plans to change/alter/fix bugs in some of the mods and reduce the amounts of plugins to load. I would be very nice if someone could tell me how modders created .esm files. Do I need to make a merged patch with the FO3edit or something?

I would be nice if someone could give me some pointers here.

You can NOT directly edit an ESM files. That is why it is a Master. You instead have to record changes with an ESP file, and when the game loads, it goes down the list, loading the masters first, that applying the changes of any ESPs.

If you want to fix bugs in mods, then set the mod as the active file and make the changes directly to it. If you want to change something in an ESM, then you HAVE TO do it through an ESP.

Well, technically you could turn the ESM into an ESP and then convert back, but that is very risky, because any error and you will have to reinstall the game. With an ESP, any error is solved by removing the mod.

Well, thank you for the answer, that helped me a lot. I just have the problem that my Fallout 3 game crashes frequently and I cant figure out why. I think I made a mistake when I installed mods or something, there where also some other stuff I needed to fix. It most annoying. Never had these issues before with the first time playing FO3 with mods and I used almost the exact mod layout I use now.

BTW: What is FO3 Master Update used for?