Sweetening after ferm.

I added sugar before first ferm and after siphoning it today I tasted it and it was a lil tart. My question is am I able to added sugar now without affecting anything but having a sweeter taste? This is first try for me so thanks for help in advance.

You could add sugar to taste and then refrigerate the cider to prevent renewed fermentation. There are other options as well in regards to using sorbate or artificial sweeteners that yeasties don't like to eat. How do you plan to store the cider? Are you planning to carbonate it?

I would suggest using sorbate. It is used in wine making to stop fermentation before it is complete or prevent fermentation from starting again when back sweetening. Once it is added you can back sweeten to your taste without worry of fermentation restart.

I've tried xylitol (birch sugar alcohol) with decent results as a nonfermentable sugar. It's nice because it doesn't have an aftertaste that I can detect in small amounts - and I'm usually extremely picky on that - and because you can still bottle carb if you're looking for fizzy cider...which I'm kinda assuming you are!

Otherwise you can always sweeten in the glass...juices or syrups could be interesting, and you could always experiment with different flavors then too...

This is my first time so only made a gallon so I can get taste right before making bigger amounts. I was just going to store it in glass bottle. Is this right? And want to carb it but still have to read up on that.

Or You can sweeten with non fermentable sugars like candarel, lactose(not real sweet, but takes of the edge) or perhaps stevia (no experience with that one though)