Update, the previous example did not work completely correct, it sometimes (first time) came up with the old answer.

I changed the thing to do to user find to reset the instance.
    @RequestParameter 
     public void setMdaIcnMonthsId(Long mdaIcnMonthsId) {
         if (mdaIcnMonthsId != null)
              if (this.getConversation().isLongRunning())
                   if (this.instance != null)
                        if (this.instance.getKey() != null)
                             if (this.instance.getKey().compareTo(mdaIcnMonthsId) != 0 )
                                  this.instance = getEntityManager().find(MdaIcnMonths.class, mdaIcnMonthsId);

          this.mdaIcnMonthsId = mdaIcnMonthsId;
     }

Is this a correct thing to do?

The code is created with Seam-Create new entity.

List to select the object:

    <h:form id="mdaIcnMonthsForm">

        <rich:panel>
            <f:facet name="header">mdaIcnMonths for month #{mdaIcnMonthsHome.instance.stmPerPeriodsR.month}</f:facet>
    
            <s:decorate id="nameDecoration" template="layout/edit.xhtml" for="name">
                <ui:define name="label">DollarExchangeRate</ui:define>
                <h:inputText id="name" required="true"
                             value="#{mdaIcnMonthsHome.instance.dollarExchangeRate}" rendered="#{s:hasRole('MDA_DOLLAR_USER')}"/>
                <h:outputText value="#{mdaIcnMonthsHome.instance.dollarExchangeRate}" rendered="#{!s:hasRole('MDA_DOLLAR_USER')}"/>
            </s:decorate>
            
            <div style="clear:both"/>
            
        </rich:panel>

        <div class="actionButtons">
            <h:commandButton id="update" 
                          value="Save" 
                         action="#{mdaIcnMonthsHome.update}"
                       rendered="#{mdaIcnMonthsHome.managed and s:hasRole('MDA_DOLLAR_USER')}"/>                  
            <s:button propagation="end" 
                               id="done" 
                            value="Done"
                             view="/mdaIcnMonthsList.xhtml"/> 
        </div>
    </h:form>

The home object is also standard

@Name("mdaIcnMonthsHome")
public class MdaIcnMonthsHome extends EntityHome<MdaIcnMonths>
{
    @RequestParameter 
    Long mdaIcnMonthsId;

    @Override
    public Object getId() 
    { 
        if (mdaIcnMonthsId==null)
        {
            return super.getId();
        }
        else
        {
            return mdaIcnMonthsId;
        }
    }
    
    @Override @Begin
    public void create() {
        super.create();
    }
    

     @Override
     @Restrict("#{s:hasRole('MDA_DOLLAR_USER'}")
     public String persist() {
          // TODO Auto-generated method stub
          return super.persist();
     }
      
}

Sorry, missed the list page:

           <h:dataTable id="mdaIcnMonthsList" var="mdaIcnMonths"
                      value="#{mdaIcnMonthsList.resultList}" 
                   rendered="#{not empty mdaIcnMonthsList.resultList}">
 
                 <h:column>
                    <f:facet name="header">Month</f:facet>
                    <s:link id="name" 
                         value="#{mdaIcnMonths.stmPerPeriodsR.month} " 
                         view="/mdaIcnMonths.xhtml" >
                        <f:param name="mdaIcnMonthsId"  
                                value="#{mdaIcnMonths.key}"/>
                    </s:link>
                </h:column>