IBM ESQL dynamically access to fields

i need to access to a field using variable,

1. 
   

   i have the enviroment variable containing the path of the field i need to modify es. SET Environment.Variabili.Mappings.mapping[1].xpath='trades.trade[1].id';

   
   


2. 
   

   i want to modify the value of this field usinng the enviroment variable es.SET OutputRoot.XML.MxML.{Environment.Variabili.Mappings.mapping[1].xpath}='test';

   
   

But it does not modify the field but it create an other field like this:

<MxML>
  ...
  ...
  ...
  <trades.trade[1].id>test</trades.trade[1].id>
<MxML>

Is it possible to dynamically acces to the XML field?

Ty. Regards.