Is there a difference between the grocery store package of chow mein noodles and the package of lo mein noodles?
It becomes quite confusing when talking about the difference between chow mein and lo mein mainly due to the error in translation. 

In Chinese chow mein literally translate as "fried noodles." However when buying chow mein at a chinese restaurant, you get vegetables with a side of deep fried noodles. Somehow the title of a dish is referring the to side rather than the main dish which leads to much confusion.

When talking about chow mein at a grocery store, it also gets confusing because you can get two types of noodles. The first kind is a fried noodle that looks something like this:



This is definitely not what your recipe is referring to. The second type of chow mein you will find is very much similar to lo mein. It should be a raw noodles that is still semi-soft. It should look like this:



If the chow mein you have at your grocery store resembles the second type of noodle, then you may use that as a substitute. If it resembles the first type, don't. The first type is used as a topping sort of like chinese croutons.