For first part of your question, the answer should theoretically be yes. Upgrade and outright redemption falls into the same fare bucket (U class for business). To be safe, give CX a call to find out. They can check upgrade availability on the spot and will most likely tell you "we recommend you buy your PEY ticket asap to secure the upgrade while space lasts".

As for the second class, others would know more but I don't see why you can't make changes to other sectors of the itinerary.