I cant edit some of my plugins

Some plugins have you go in the files to change things like this plugin https://dev.bukkit.org/projects/advanced-achievements you have to go to the files to make more achievements but something like this plugin https://www.spigotmc.org/resou…lugin-1-8-x-1-14-x.67345/ lets you go in the files but why is it that you can only use the files on some plugins. we need a way to use he files on all plugins.