I wanted to define some new buttons for my scripting trials.
I altered th 1st line -
<buttonpanel id="1" rows="5" cols="8">I added the blue code, leaving some original code from 4/8 in place as a place holder
 <button row="4" col="8" modifier="none" acceptfiledrop="0" label="#{b,50}" cmdtype="1">
    <desc>#{b,50}</desc>
    <command options="0">Core.1070</command>
  </button>
   <button row="5" col="1" modifier="none" acceptfiledrop="0" label="#{b,50}" cmdtype="1">
    <desc>#{b,50}</desc>
    <command options="0">Core.1070</command>
  </button>
 <button row="5" col="2" modifier="none" acceptfiledrop="0" label="#{b,50}" cmdtype="1">
    <desc>#{b,50}</desc>
    <command options="0">Core.1070</command>
  </button>
 <button row="5" col="3" modifier="none" acceptfiledrop="0" label="#{b,50}" cmdtype="1">
    <desc>#{b,50}</desc>
    <command options="0">Core.1070</command>
  </button>
 <button row="5" col="4" modifier="none" acceptfiledrop="0" label="#{b,50}" cmdtype="1">
    <desc>#{b,50}</desc>
    <command options="0">Core.1070</command>
  </button>
 <button row="5" col="5" modifier="none" acceptfiledrop="0" label="#{b,50}" cmdtype="1">
    <desc>#{b,50}</desc>
    <command options="0">Core.1070</command>
  </button>
 <button row="5" col="6" modifier="none" acceptfiledrop="0" label="#{b,50}" cmdtype="1">
    <desc>#{b,50}</desc>
    <command options="0">Core.1070</command>
  </button>
 <button row="5" col="7" modifier="none" acceptfiledrop="0" label="#{b,50}" cmdtype="1">
    <desc>#{b,50}</desc>
    <command options="0">Core.1070</command>
  </button>
 <button row="5" col="8" modifier="none" acceptfiledrop="0" label="#{b,50}" cmdtype="1">
    <desc>#{b,50}</desc>
    <command options="0">Core.1070</command>
  </button>  </buttonpanel>
Can't get it to work tho, I still have my original 4 rows - I did restart MC, maybe my install is flaky, or I'm going mad....  
