First Question are you using Autocad or similar CAD ?
and second issue please check the Option selected on Tools reference on Excel Development Area see picture
All attributes are stored in AttributeList array, during routine debug you can check which is the attributes you need to change see picture above, check the properties AttributeList(XX).TAGSTRING for information on NAME of Attribute and AttributeList(XX).TEXSTRING for modification.
For modification you can insert:
If AttributeList(6).TEXTSTRING="C####-E-000" then ' DRAWINGNO SHALL BE at position 6 of AttributeList array check with debug.
AttributeList(6).TEXTSTRING="C1234-E-000"
end if
Of course Attribute value it's a string so you can manipulate as you need, it's could be from excel cell value, or LEFT("XXX", CharPos) or MID, or RIGHT.
I understand that you have to run the program and "watch" the attributes to see the full list of them all, but when i try , it doesn't appear in a list like what you get. I'm probably doing something wrong, i've not got much experience with VBA yet
and type function key F9 so you insert a break (you will see a red row) of procedure when it is running and will pass on that point of code.
Run the procedure and when break point will be reached click with right mouse button and select add watch option.
On VBA software you will have a debug windows where you can see the "watched" variable. Click on the + sign on visible variable on that window and you will have all properties of selected variable (see picture on previous post).
Search the attributes name in TAGSTRING property value, and then you can modify the TEXTSTRING property value for change it as I showed you before.
Let the procedure execute the code in row because when you break on a specific row this will be not executed.
Press F8 function key and watch again. And press F5 to run again until next breakpoint will be reached again.