ok, i figured it out:

call to sub:

%test = &before_modify_multi_record(%{$modify_rec{$key}});

sub:
my (%rec3) = @_;

i kept having a problem and thought this was the cause. however, finally traced my problem to something else so this was actually not complicated at all. all seems to be working now. if you see something that looks wrong, pls let me know!