s/
\{name_a
    (
        (?:
            [^=\s]+ =  "[^"]*"
            |
            \s+
        )+
    )
\}/ FunAt($1) /gex;

sub FunAt {
    join '', '{name_a ', AtAt(@_) ,'}';
}

sub AtAt {
    my %fun = $_[0] =~ m/([^=\s]+) =  ("[^"]*")/gx;
    return join ' ', map { "$_=$fun{$_}" } grep /param_[xy]/, keys %fun;
}