Thanks for your answers! And sorry about the delay.
You can supply required settings in a tweak ini file loaded by the Miranda.
The info is a bit much limited, but I have seen what you are talking about (the mirandaboot.ini file). Luckily there are good descriptions included, so it is possible to do what I wanted to achieve. I'm showing the necessary steps to do the same (in my case for a Jabber account):
1. Download the Database Editor++ (
http://wiki.miranda-ng.org/index.php?title=Plugin:DbEditorPP/en) and add the dll file to Miranda NGs "Plugins" folder.
2. Start up Miranda NG and click on the registry icon button called "Open Database editor". If the desired Jabber account doesn't exist already, create one now.
3. Extend the "Settings" entry and you will see an entry called "JABBER_1". The Jabber account settings are stored here. Right click it and click on "Export" and then save the ini file.
4. If you would like to apply all settings to a copy of Miranda NG, it's enough to rename the file to autoexec_forced_jabber.ini (name style has to be autoexec_forced_*.ini). Place this ini file into Mirandas main folder.
In my case, I have adjusted the file to include just these settings. The main benefit here is, that no account will show up, but these settings are applied to a new one anyway!
Spoiler
SETTINGS:
[JABBER_1]
BsDirectAddr=u
BsDirectManual=b0
BsDirect=b0
BsProxyManual=b0
MsgAck=b1
EnableAvatars=b1
LogChatstates=b0
LogPresence=b1
LogPresenceErrors=b0
EnableUserMood=b1
EnableUserTune=b0
EnableUserActivity=b1
AcceptNotes=b1
AutosaveNotes=b0
EnableMsgArchive=b0
Disable3920auth=b0
EnableZlib=b1
EnableRemoteControl=b0
ShowTransport=b1
AutoAdd=b1
AutoAcceptAuthorization=b0
FixIncorrectTimestamps=b1
DisableFrame=b1
ProcessXMPPLinks=b0
IgnoreRosterGroups=b0
AllowVersionRequests=b1
ShowOSVersion=b1
BsOnlyIBB=b0
AcceptHttpAuth=b1
5. Miranda NG is going to warn you about the changes. To avoid this warning, edit the mirandaboot.ini file and change the warn setting to "onlyunsafe". I don't know if this is a clever idea to change this, so keep in mind that it could be unsafe, if a harmful program places an ini file there.
6. Done. The settings are successfully applied. If you got trouble to find your desired setting in the database editor, there is a trick: Export
all settings via the database editor, change your desired values, and then export the settings again. Now you can use a program like WinMerge to compare both text files.
I'm hoping this text is helpful to someone else and understandable.
So, to answer the question:No, it's not possible right now.
Okay, good to know that it isn't officially supported in an easy way. With my method it's actually working, but it's more like a workaround. Because if the user decides to delete the account in Miranda NG, and creates a new one, then these predefined settings are gone. Unless the ini settings file is applied at every start up, but that's not the most elegant way...