<CLASS DOES NOT EXIST>%Close...
is typical if try to access resultset or just delete rset  after leaving namespace %SYS.
Just reproduced it.

%SYS>w !,rset.%Next(),?5,rset.%Get("Directory"),!?30,rset.%Get("Size"),?40,rset.%Get("MaxSize")
 1    c:\intersystems\iris\mgr\enslib\
                              163       Unbegrenzt
%SYS>ZN "USER" 
USER>k rset
<CLASS DOES NOT EXIST>%CloseCursor+3^%SQL.ClassQueryResultSet.1 *SYS.Database
USER>

#1 there is no "SELECT LAST_SERIAL()" 

#2 depending what your expectation on LAST is I see 2 possible workarounds
#2A LAST = max:    "SELECT MAX(test_id) FROM test" 
#2B LAST = latest: "SELECT test_id, MAX(ID) FROM test GROUP BY  2"

#2B is based on the fact that you always have an  auto-incremented ID and it's a shortcut of
"SELECT test_id  FROM test where id = (SELECT max(ID) from junior.test)"
or
"SELECT TOP 1 test_id FROM test WHERE ID < 999999999999999999 ORDER BY ID DESC" 

So, as by docs. 

SQLCODE=100 indicates that the SQL operation was successful,
but found no data to act upon

https://docs.intersystems.com/iris20201/csp/docbook/Doc.View.cls?KEY=RERR_sql#RERR_sql_noerr

There is my example in OEX:  Light weight EXCEL download

if you omit the special setting of type, it is a normal html table.
 

What I asked for:

In your Method written in Objectscript, after 
&sql(update X_X.X  set LocalEnvironment=1 where %ConfigName IN('X_X_X', 'Y_Y_Y'))

Variable SQLCODE holds a success / failure code.  That's what I asked for.
see this example: 
https://docs.intersystems.com/iris20201/csp/docbook/Doc.View.cls?KEY=GSQL_esql#GSQL_esql_syntax_ampsql
or 
https://docs.intersystems.com/iris20201/csp/docbook/Doc.View.cls?KEY=GSQL_esql#GSQL_esql_code_literals
and
https://docs.intersystems.com/iris20201/csp/docbook/DocBook.UI.Page.cls?KEY=RERR_sql#RERR_C136606

You may stick with '/' and run $TRANSLATE(record,"/","~")
just before writing the record to your file.DAT

All %R* routines are hidden in IRIS for good reasons.
And they just survived for backward compatibility not for common use.
And they use ZS ZI, ...  and $Compile() function. ... and a bunch of $ZU(..)  
Manipulating routines from Terminal is not covered. VScode or Studio is expected and supported 

If you edit .INT routines from the terminal in the old MUMPS style using
             ZLOAD, ZSAVE, edit by  X ^%
you operate at a lower level than Studio, VScode, Atelier,... 
and deeper than any Source Control Hooks. 
Neither belt nor suspenders are available anymore.

It's like heart surgery: Either you fix it or your patient is gone.