Regarding "patch sizes". If you have a correction to make to an object (not the media), like adding an effect in your case, you can make a NEW bank with only the modified object in it (no media, no event, removed in the SoundBank Editor). The bank will be tiny. Deploy that bank and make sure to load the new bank before the old banks. Tadam! The new version of the object will take precedence over the old. That said, you do need code in your game to be able to find and load said new bank. Check the DLC articles in the documentation.
You will not be able to use the Time Stretch on a bus, even if you set it programatically. There is a reason why the UI doesn't allow it :) Conceptually, the sound sources push the sound to the bus for mixing, and then the effects of the bus are applied. The TimeStretch effect changes the time referential. So, if you accelerate time, your input will still be pushed at the same rate but the output would be shorter: you now have an audio gap every frame. Conversely, if you slow time, the Time Stretch will make the output longer, which still needs to be mixed with other busses that are not time stretched. Therefore, it would mix the appropriate number of samples with respect to the output sample rate, and a remainder would need to be carried over to the next audio frame. Each second of playback, you'd accumulate a growing backlog of unplayed audio... Soon enough you won't have enough memory. On ordinary sounds, you don't have this issue because the source is definitively finite in time.