Is there a way to rescale an assembly without have to go to each part model and rescaling them individually?
Depends on the end result required. What are you actually trying to achieve?
You could save the assy as a part and then use the Scale tool.
You could modify the ModelRescaler macro from http://www.lennyworks.com/solidworks/default.asp?ID=20 to iterate through the assy and scale the components automatically.
EDIT: This assumes the component parts are fully dimensioned.
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