Is it possible to reset a property value something like:
myProperty=myProperty.Defalt
Not unless you add code to remember the initial state so you can reset it
So, is there a war to do it without storing another Property or variable?
Yes, set the property to the value you entered as default at design time… Should not be too difficult to remember 
Doh.! That will work.
I guess it would be smart to put a note in the comment of the Property that there is code that need to be updated if the property is ever changed.
Use a constant so you only have one place to make the change. (Did you know that you can use constants in the Inspector to set the value?)