The entry point to a program in C # is the Main method. This method must be static. Static elements of a class or structure are independent program units, do not require an instance to call and, in fact, use the name of the class or structure in which they are declared only to extend their own name and ensure its uniqueness. Static members are not inherited, they cannot be abstract or virtual, you can even write completely in a procedural style, using only static classes and their elements.
The structure is essentially a class, but with disabilities, in which at the language level some principles of OOP are forbidden (inheritance from other classes or structures is prohibited, but the implementation of interfaces is allowed, the rest is the consequence). Well, yes, the structures are related to ValueType, which imposes some more restrictions, but at the same time, makes it impossible for classes to be available. However, in terms of static elements, the structure does not differ from the classes, except that the structure itself cannot be static.
Therefore, from the point of view of the CLR, there is no difference to which the Main method will be attached, and there will be no consequences from such a replacement. Another question. how you will use this class or structure in the future, but this is really another question.