pipe exspanshion

Does it matter if the pipe is exspanded to let anouther pipe fit in or can the end of my muffler be exspanded to alow the pipe to slide in.I am working with 2/1/2 inch pipe.i just bought 10 foot of flexable pipe to make up a template than i will take the pipe to a shop were they can bend the pipe the same as the template.Any thoughts