For the default view of all computers, the file to change is ms_all_computers.php, lines list_fields2 = and default_fields2 =, adding e.g.
$l->g(65) => "h.model",
to list_fields2 and including in default_fields2:
$l->g(65) => $l->g(65)
And for administrative columns, adding in list_fields2 something like these (label 1620 is not used for ocs):
$l->g(1620) => "fields_36",
and adding the respective labels in en_GB.txt and in es_ES.txt, for example.
For multi search I found that the lines to change are public $defaultFields = in Search.php, like this:
public $defaultFields = [
"hardware.ID", (default)
"hardware.DEVICEID", (default)
"hardware.NAME", (default)
"hardware.WORKGROUP", (default)
"hardware.OSNAME", (default)
"softwares.NAME", (added)
"softwares.VERSION", (added)
"monitors.CAPTION", (added)
];