Can evaporated milk be converted to "regular" milk?
Yes, you could certainly reconstitute evaporated milk by adding water. 

The outcome would give you similar but not identical results as fresh milk, due to the change in flavor the milk underwent while being cooked down to the evaporated state:  it will retain the slightly cooked, caramelized flavor.  This may or many not have a significant effect on a given recipe.

Milk also freezes, and still is suitable for most cooking purposes, should you choose to do so.

Finally, if you use milk very rarely, unless you are making a dairy dominated recipe like custard or cream soup, you may not have to use milk at all.  Water or another liquid might perform similarly or well enough&mdash;it depends on the specific application.