125-200cc SM 125 Tuning

Hello guys ,do you know what will happen if i change only the ehxaust silencer and leave the other exhaust original , will it split oil on the swingarm ,will it change the power or something ?
Also what will happen if i change the whole exhaust ( problems etc ) and what exhaust do you recomend .
Also what other changes will i have to do ( i have the 2007 oil injected sm )?
And finally i scratched the original aluminium silencer , anyone know how can i fix it ?
thanks in advance