Transaction Service Call Example Needed to change a value

I am looking to increment CPY-LAST-BATCH by one.  I've been mostly doing DME calls which is supposedly read only.  This is my first attempt at a transaction.

To my understanding, we have to do an FC=I first, than an FC=C with the new value...

             '_PDL=LSAPPS' +
             '&_TKN=AP00.4' +
             '&_EVT=CHG' +
             '&_RTN=SENT' +
             '&_LFN=ALL' +
             '&_TDS=IGNORE' +
             '&FC=I' +                  // I=Inquire, C=Change
             '&CPY-COMPANY=100' +       // Company (Key)
             '&CPY-LAST-BATCH' +        // Last Batch Number
             '&_OUT=XML' +
             '&_EOT=TRUE' ;  

             '_PDL=LSAPPS' +
             '&_TKN=AP00.4' +
             '&_EVT=CHG' +
             '&_RTN=SENT' +
             '&_LFN=ALL' +
             '&_TDS=IGNORE' +
             '&FC=C' +                  // I=Inquire, C=Change
             '&CPY-COMPANY=100' +       // Company (Key)
             '&CPY-LAST-BATCH=1010101' +        // Last Batch Number
             '&_OUT=XML' +
             '&_EOT=TRUE' ;  

However, I am getting an error stating that "Tax code not setup for company".  Am I supposed to include that information again when I just want to just change one field?  

Also, is there a way to lock the record from read to write to prevent more than one person from changing a value at the same time?