This is tricky, because there are a ton of questions with only the vmware tag -- 1,090 as of the time I originally wrote this.
Note the sidebar where it says "related tags", pay close attention to this Related Tags sidebar:
- vmware-esx × 146
- virtualization × 144
- vmware-esxi × 111
- linux × 74
- networking × 63
- windows × 59
As for the idea of "rename the tag if the text contains x", I downloaded a copy of the server fault database and ran some queries:
- questions with only the vmware tag, and no other vmware related tags: 725
- of the above, with the string "esx" or "esxi" in the body or title: 157
That leaves ~568 questions (!) needing manual retagging. That's .. a lot. Really a lot.
edit: I have done the following, just now
when a question was tagged vmware only, and its body or title contained "esxi", I converted that tag to vmware-esxi (70 questions)
when a question was tagged vmware only, and its body or title contained "esx", I converted that tag to vmware-esx (92 questions)
when a question contained both vmware and vmware-esx or vmware-esxi, I removed the vmware tag so the more specific tag can be primary. (~250 questions)
Beyond that am I at a loss as how to proceed..