Now there is -Ppodio:output_include_collections and if any value is written there it overrides full default list which now has ~60 names in it. In some cases it is very desired behavior and this should not be changed. But there should be a way to save additional data collections, which are not saved by default in addition to the default list.

Something like this:

# no flag means all 60 default collections will be written (if exists)
eicrecon

# only MCParticles and ReconstructedChargedParticles are saved (no other 60 default values)
eicrecon -Ppodio:output_include_collections=MCParticles,ReconstructedChargedParticles

# new proposed flag
# now MyCustomCollection in addition to all default collections are saved
eicrecon -Ppodio:add_output_collections=MyCustomCollection

P.S. And not sure add_output_collections is a good name