Anbody know if I can reuse my stock 02 sensor without any codes being thrown if I get a high flow cat?

 

You should be ok.

 

yup, no problem. if you should happen to start getting codes, have an o2 extender put in. it makes the hole smaller so as to trick the sensor... but you should not need it. ive gone 75k miles with 2.5 inch exhaust and a high flow cat. but every engine is different and so is the environment that the engine runs in.