Yes you can do this with a case statement, so assuming your graph is currently produced like this, where the numbers are in afield call 'line':
| stats count by line
You could then do this, defaulting back to the number if you haven't set a value:
| eval text=case(line=="181","text_for_181",line=="211","text_for_211",line=="212","maxis",line==42","text_for_42",1==1,line)
| stats count by text
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