I've try to make some MODS but every time this game update it's patch...I have to start over and I can't finish it. What if I offline stream every time before I start game? Will it stop update? I just want to finish all MOD once time.
Make a copy of the stardew valley folder and place it elsewhere. It's DRM-free so you can launch it outside of steam. Then you can overwrite it personally whenever you want. There's also an option on steam to exclude updates for games individually by right-clicking the title and choosing properties.
I haven't play this game for a very long time until I finish 50% of my custom mod...But when I try to test them, Then it update...
Otherwise, if your mods works through XNB files, you can use XNB loader to use your custom files instead of replacing the ones in the Content folder. https://community.playstarbound.com/resources/smapi-xnb-loader.4506/