Go for it, it shouldn't be too hard.  <code>XMLElementInt</code> is just a subclass of <code>XMLElement</code> with some special value handling jammed in. I would recommend against trying to use regular-expressions to do this for performance/resource reasons.  I'm not sure if the <code>autotest-framework</code> has any code for parsing/validating hex-strings, it's worth checking.  

The important thing is that they are represented in the XML in hex, so accepting integer input and string-format converting it is fine.  Going the other way (hex string to int), the only way I'm aware of is using <code>eval()</code> (which is ugly).  Hopefully you can find a better way.