major problems

i have a 94 jetta gl need to know if i can bore out my cadilidic converter or will it mess up my o2 sensor

Yes you will cause problems to your O2 sensor. if you want to get some HP you will need money to buy a bigger pipes with the correct cat. I recommend speedy.com or thepartsbin.com if you need a new exhaust.

Since you only have one O2 sensor before the cat it won't affect the sensor & won't turn on a check engine light. However, this is illegal to do as it will no longer meet emmissions requirements. If you live in an area that does tail pipe emmissions testing they will be able to tell the cat is not functioning.

i hollowed out my cat because it was falling apart i have a 94 jetta gls n it didnt effect my o2 sensor at all but from time to time it comes on just cause of carbon build up... but it goes off a second later