Dropping relation information

We are trying to convert a treebank.

Input:

# sent_id = DW-s2
# text[seg] = Wiñarqu -y -manta -wan miryukuna -manta -wan 
1	Wiñarqu	_	VERB	Root	_	3	s.arg	_	Gloss=desarollar,crecer
2	-y	_	NS	NS	VerbForm=Inf	1	ns	_	_
3	-manta	_	Cas	Cas	Case=Abl	6	@conj	_	_
4	-wan	_	Cas	Cas	Case=Ins	3	s.co	_	_
5	miryukuna	_	NUM	Root	Number=Plur	6	s.arg	_	_
6	-manta	_	Cas	Cas	Case=Abl	0	sntc	_	_
7	-wan	_	Cas	Cas	Case=Ins	6	s.co	_	_

grs:

rule mergens {
  pattern {
    V [xpos=Root];
    NS [upos=NS];
    V -[ns]-> NS;
  }

  commands {
    V.form = V.form + NS.form;
    V.VerbForm = NS.VerbForm;

    del_node NS;
  }
}

rule cas { 
  pattern {
    R [xpos=Root];
    C [upos=Cas];
    C -[s.arg]-> R;
  }
  commands{
    R.form = R.form + C.form;
    R.Case = C.Case;
    
    del_node C
  }
}

strat main { Seq (Onf(mergens), Onf(cas)) }

Output:

# sent_id = DW-s2
# text[seg] = Wiñarqu -y -manta -wan miryukuna -manta -wan 
1	Wiñarqu-y-manta	_	VERB	Root	Case=Abl|VerbForm=Inf	_	_	_	Gloss=desarollar,crecer
2	-wan	_	Cas	Cas	Case=Ins	_	_	_	_
3	miryukuna-manta	_	NUM	Root	Case=Abl|Number=Plur	_	_	_	_
4	-wan	_	Cas	Cas	Case=Ins	_	_	_	_

As you can see, the head and relation information is lost. Is there a way to preserve or update this information in my commands?