Called again. Tried to get agent to ticket return using United on the return again, but this time using a flight that is actually AC marketed, AC 5961 FRA-SFO. Denied, since agent could only see flight if I flew on to YVR. (I tried to make the flight go back to SFO, but alas, there were no more connections thatr day).

Decided to give up arguing with AC and just take an SFO routing. Decided to try out LH new biz class out of Munich instead of trying to get United p.s., which I decided was a lost cause. This would involve booking a LH coded segment operated by Air Dolomiti, which I hoped the agent would have no issue with.

This time, the whole deal proceeded quite painlessly and I was issued a
SFO-YYZ-CDG/VCE-MUC-YYZ-SFO
routing no problem, even with the LH coded segment.

The MUC-YYZ segment issued in D, which is perfect, because D on LH credits 200% on my preferred FF program!

So here's the conclusion out of the whole thing:

- Air Canada reps are very inconsistent over the phone.

- The time of day affects which call center you get (assuming you don't call directly into int'l call centers). I called at 2AM pacific and got someone from YSJ (at least thats where my ticket was apparently issued). It seems that Tampa call center agents are very note-happy.

- Do not ever tell AC you want a route for miles. It will result in a note on your PNR and any agent who reads the note will be very cautious to not give you extra segments.

- You can change starting/ending cities to cities within 200mi

- For a int'l flight, you can change your flight +/- 3 days pretty easily... The agent will start asking you questions if you exceed this... The guidelines indicate the maximum is +/- 7 days.

- Any pure AC routing will generally be permitted, as long as you are traveling in one direction (i.e., not forming circles). You can change both the inbound/outbound, even if only one flight was affected.

- Any AC marketed flight is permitted, so long as you fly the entire marketed flight (for example, they will not allow you to fly only the FRA-SFO segment of a FRA-SFO-YVR routing).

- OAL is allowed on short haul only. They don't have to be *A. I was able to get a US airways flight and a LH coded flight without issues.

- Its supposed to be possible for them to book OAL on long hauls which are not AC marketed, especially when the only AC route is inefficient or results in an overnight. This might take quite a bit of work and being careful to not get your account notated.

-Maybe the reason AC wait is so long on the phone (>30 min to talk to an agent??? really???) is that you can't even do basic things like fix your booking after a schedule change online...

Well, it was an interesting experience. And it has also taught me that sometimes, people on this forum can post wrong or speculative answers based on their experience (but more often than not they are right!) and sometimes, you just need to check everything yourself. By the way, thanks everyone for the help! Maybe I will write a what to do if your AC schedule changes thread one day.