I believe a lot of the rebooking depends on who you speak to, and how you speak to them. In IRROPS, I categorise people are 4 distinct group of avenues of support.

Group A - The staff holding the new boarding passes at the arrival gate/Gate agent if IRROPS for departure flight.
Group B - The staff at the transfer desk
Group C - The staff in the lounge (Not applicable for Chinese Carriers, their lounge staff have no access to reservation systems
Group D - Airline Call Centre / Airport Ticketing office

Group A is generally useless if you don't want what they have given you. They are there as human messengers. That's it. No decision making power, and probably don't even know how to use the system to rebook you.

Group B is a hit of miss. Depends a lot on how you speak to them. If you talk to them like they owe you a living, then be prepared for them to politely smile and say they can't do anything. If you sweet talk them, I have seen some go the extra mile to get things done.

Group C really depends on the airline lounge capability. It has to be an airline directly operated lounge like SQ/CX etc. I've had a lot of help from these people, especially in the US. The good old days when it was called the Red Carpet Club.

Group D can also be really helpful, especially call centre if you are not in an airline hub. I remember plane went AOG ex-SIN, the transfer desk in SG would only rebook me to the next SIN-KUL-PVG, arriving 16 hours later. Called the call centre, and they put me on SQ direct to PVG, and all I had to do was to go to the SKL to collect my BP. Of course, I had to stress to the agent that I was HBO before they were willing to rebook me as the SQ PVG flight was departing in 75mins.

The last time, I had LO WAW-MXP-SIN, with WAW-MXP cancelled, they re-booked me on Lufthansa. Wasn't happy so I went to the airport ticket office that had me go via LHR but with an overnight as 319, 321 was full. When I arrived at LHR, I went to the SQ check in desk, and they were happy dig my bags out, and put me on standby for 319 and 321. Eventually offered to be let into departure to try to make 319, with the caveat that if the bags don't make it on 319, i could be denied boarding. When I got to 319 boarding gate, they said they still could not get the bags, but were working on an exception for bags to go later, and asked that I board first, but might be asked to leave the plane if the bags don't make it. Eventually the agent boarded the plane and came to my seat to tell me that the bags made it. All of these on a ticket issued on LO stock.

So it's really a matter of how willing someone is to help.