new source to build your satellites.xml files.

[AlexWilMac]

OK, today I had more time to go deeper into this field I had never approached before. And, @Matrix10, it's more clear to meant in some post, although there a new question.
I restored the original satellites.xml and there the problem is the same than in my file: the same transponders I couldn't use as "predefined" are not in the original satellites.xml as well.
And I see that are available (either in signal finder or in automatic scan by predefined transponders) all those transponders where you have
system="0" modulation="1"

For, instance, posting here just a few about 13°E (as I said: this is now the original file, not the customised one):
<transponder frequency="10719000" symbol_rate="27500000" polarization="1" fec_inner="3" system="1" modulation="2"/>
<transponder frequency="10727000" symbol_rate="30000000" polarization="0" fec_inner="3" system="1" modulation="2"/>
<transponder frequency="10758000" symbol_rate="27500000" polarization="1" fec_inner="3" system="1" modulation="2"/>
<transponder frequency="10775000" symbol_rate="27500000" polarization="0" fec_inner="4" system="0" modulation="1"/>
<transponder frequency="10796000" symbol_rate="27500000" polarization="1" fec_inner="3" system="1" modulation="2"/>
<transponder frequency="10815000" symbol_rate="27500000" polarization="0" fec_inner="4" system="0" modulation="1"/>

only the 4th (10775) and the 6th (10815) are shown in the GUI.
So, here we don't even have the options
pilot="2" rolloff="0"
but what makes the difference are system and modulation.
So I edited these values and (after a simple GUI restart) I was able to see them among the predefined transponders. Only...

only that I see, now, that the ones listed as system="1" modulation="2" are the DVB-S2 ones, whilst the system="0" modulation="1" are the traditional DVB-S ones.
The conclusion seems to be that you can't see the DVB-S2 transponders available for signal finder or for a scan by predefined transponders not because you can't have in the satellites.xml file or because there's a problem with it but simply because DVB-S2 transponders can be used only by a complete scan and not elsewhere.
Obviously, as always, you can tune a channel by a manual scan (that, in fact, needs a choice from the user between DVB-S and DVB-S2).

 

[Matrix10]

This confirms what I wrote earlier.
Why is that so I do not know.
A couple of years ago, there was discussion on the PLI forum related to this.
Do they change something there I do not know.
I do not use this option predefined transponder.

 

[AlexWilMac]

Yes, usually I don't use it, too but some other time I just feel lazy and don't not want to enter each parameter in the manual scan when I want to scan only a transponder...
Now I learned that if the new channel I want to add is a DVB-S2, the fastest option is the manual scan (otherwise I should perform a complete scan of that SAT). Otherwise, if the new channel is a DVB-S one I can use both (or three) ways.
And now, I also know that it is useful anyway to prepare a customised file because, at least, it speeds up the automatic scan.
In conclusion: the predefined transponders are only DVB-S but all the other ones are equally included in the satellites.xml file.