"Same day standby" is a concept largely centred on US-based airlines. For most other airlines around the world, a change is a change is a change, and if you need to pay for changes, they will charge both the change fee and any possible difference in a fare, full stop.

There are exceptions - typically if it helps the airline (ie if the flight you are booked on is overbooked, or if it has a significant planned delay which might make you miss your same-ticket connection, etc) but the default solution - especially if you have no high FF status and are travelling in a cheap booking class - is that this will not be possible.

On the question about award ticket booked on partner miles, I fully agree with the answer above, the operating airline will never touch the ticket (except in case of IRROPS) and will ask you to call US and sort it out with them.