Little ST script doing what I want:
[Gramps SuperTool script file]
version=1
[title]
Individus-Sort_as des individus groupés
[category]
People
[initial_statements]
[statements]
for n in nameobjs:
n.sort_as = -1
[filter]
[expressions]
([n.group_as, n.sort_as, n.display_as] for n in nameobjs)
[scope]
selected
[unwind_lists]
False
[commit_changes]
True
[summary_only]
False
