Are there any sugar substitutes for preserving food?
It's hard to understand what you are asking about here. 

If you mean a substitute as something you drop into an existing recipe instead of the required sugar, then no, there aren't any. 

There are other methods for preserving food instead of sugar-based ones though. So, if you don't like pumpkin jam, you can make pickled pumpkin instead. If this is what you meant, then there are "substitutes". 

There are no methods for food preservation which don't alter the taste. Freezing comes closest. It preserves flavor, but not texture.