I did a cream cheese icing batch on March 25th, I have plenty leftover, can I use it on April 10th? that like 2 weeks after, it's been in the fridge since then.
I wouldn't since it uses cream cheese, and it's been opened. I would just make a fresh batch IMHO.
If you had kept it in the freezer it would probably be okay, but in the fridge better to be safe and make a new batch.
It depends on the recipe you used. There are dozens of them out there so it's hard to say. Basically, the sugar in most recipes is enough to render it safe for at least a week. Earlene Moore has a recipe for Cr Ch B'cream that is counter safe for that long. Google her name to find it.