@Bruno, again, not quite.
So let's make sure we're talking about the same things. Mainstage has 4 hierarchical levels:
1) the Concert Level
2) the Set level
3) the Patch level
4) Channel strips
Each of these is a "container" of settings. Mainstage's "Patch Level" isn't the same as a patch/preset on a guitar effects board for example.
You can create channel strips at any level of the concert, depending on how you use them.
You can then change Channel strip settings in real time using hardware controls, at any level of the concert.
You can use Patches as a sort of "Preset", but you could also use it as a bank of sounds that you can access in real time.
There are several solutions to these, it just depends on how you want to address them.
Option 1
So let's say you have a band, and you want 1 Patch to be for 1 song, where each band member can switch sounds if they need to during the song.
1) In the patch, create each band members channel strips, and add all effects plugins to their respective channel strips that you plan on using through the song.
2) Map each effect setting that you will change during the song (i.e. guitar distortion/delay on-off) to a hardware controller using a specific channel and MIDI CC message within the patch.
3) Repeat for all other band members. Make sure that each switch is set to it's own MIDI message.
4) Within 1 patch, you can now switch distortion, delay, etc. without having to change Patches, and it will only affect that 1 parameter.
Option 2
Another idea is to have 1 song be contained in a Set, with Patches for each section of the songs. (Verse/Choruses, etc.)
1) At the set level, map a hardware footswitch to "Next Patch" and "Previous patch." For band members whose sound will be the same through the whole song, create their channel strip at the Set level.
2) Create multiple patches for each section of the song, and label them "verse" "chorus" etc."
3) Within each patch, create the channel strips for band members who need to change at the Patch level with their effects settings, and set up the effects for each section of the song. During the performance, just hit "next patch" at the right time in the song.
Option 3
Automate everything using a sequencer, and pre-plan all changes.
I just made a tutorial on how to do this if you are interested: https://www.youtube.com/watch?v=KGwlp1hpl_k