When changing oil on 496 do you all first warm the motor? If so, do you run on muff and hose? Do you run on lake prior to changing?

What are the issues with running on the garden hose?

Warm oil will be easier to drain or suck out with a pump. It's tough to put enough heat into the motor just idling on the hose, I prefer to go for a run and change the oil when I return, after flushing the motors.

I run mine on the hose and get them up to operating temperature, then do the oil change. I like doing mine this way because it gives me chance to look everything over really well and check for any unknown sounds or see any areas of concern you can't see with the hatch closed and running.

The key is to letting them run long enough to truly get some heat into the engine...as others have noted as well. bencini231 makes an excellent point...gives you a chance to look at the engine(s) whilst running and see if there are any issues.

I like doing last run of the season. But, if it has the oil drain hose that can be pulled out hull plug... let it drain into container overnight. I had to do this one season on cold engine. I even let my 496 drain overnight on warm engine too.

As long as you are not in a hurry to change the oil, you don't really need to warm it up. Just use the oil drain hose, and extend it out of the bilge drain hole, and put it into a into a jug. I had a specific 5 gallon fuel jug that I used for this task.
When I got home from a run, I'd usually let it drain out that afternoon. And then come back the next day, change the oil filter, plug the hose back up, and fill 'er up.

I used 1 quart of Lucas Oil Treatment and 7 quarts of Mobil1 15w50 for 13 seasons on my 496HOs. The boat has since had two more owners and they are doing the same; and the boat has no issues.