what are the consequences when the stock axleback muffler is installed back on this motor setup?

ej hatch
2.0L non-vtec b20b na
custom ram (cold) air intake system
stage 2 cams / sk2 cam gears (dyno tuned)
4-2-1 header / hi-flow cat / itr midpipe / fireball axleback muffler
itr clutch/flywheel/etc...

this setup was dyno tuned with the fireball muffler.

now the stock axle back muffler is installed back on.

besides performance, exhaust gases suffocatoin and a little more engine vibration what else will it hurt?

will the stock muffler actually restrict so much exhaust gases that it will be push back to the header and physicaly damaged the motor? (thats why the engine vibrates more?)

what do u think?
will the stock muffler actually damage the motor? or just plainly hurt the performance of the engine?

any comments or input will help.

thank you.

(mod, feel free to move this if its in the wrong section)

----> please post all comments/inputs on this thread