Sage,
There is no good reason that they should have any difficulty controlling your pain post-op. Your dose is so low there should be no problems.
Even if your dose were high, there should still be no problem, but unfortunately we do run across opiophobes once in awhile.
Which doc is the one that mentioned you should cut down on the oxy? Will that doc have anything to do with your pain control in the hospital? If so, then you need to take care of that now.
The best idea is to have a plan, as Boxerluver wrote. That includes forming a team to support you. And that team starts with the anesthetist. You need to clearly communicate your current meds and your concerns to him/her. If he/she will not be responsible for your post-op pain control after surgery, then you need to educate whomever that doc is about your needs.
First, you should receive your daily allowance of CP meds without hesitation, on schedule. You should not have to ask for them, they should be given automatically. Second, they should provide plenty of meds to handle the post-op pain. Do not let them try to tell you that your CP meds should handle that. They need to know that the CP meds get you to what others would consider normal. As Boxerluver wrote, the post-op pain is usually covered by a PCA (patient controlled analgesia) pump. This is an infusion of meds IV, some deliver an automatic amount per a schedule, while allowing you to hit a button when you need meds for post-op BT pain. Some just use the button push approach. However they do it, you need your normal CP meds, and meds for post-op pain after the epidural is removed.
See is the hospital has pain or patient advocates on site and contact them to ensure you are doing everything possible to get your pain needs taken care of. Write down their names so someone who watches you while in the hospital can contact them if needed.
Get a support team signed-up and you'll be fine. We're all here for you.
steve