that block needs to be exploded for modification

Why not refedit ?

I'm trying to do something similar, in plain AutoCAD - linking a label block with attributes to a special line having xdata storing the handle of the block. Not sure if I'm doing it the same way, as I don't quite understand the issue of "one reactor" vs. hundreds. I have this reactor, which I assign to the line:
(defun xxxx_reactor (obj)
  (vlr-pers (vlr-object-reactor (list obj) nil
              '((:vlr-modified . xxxx_modified))
  ))
)
Seems to work fine, for very many items. Now the problem:
Once an entire plan (1st floor, 2nd floor, roof) is done, that plan wants to be made into a block. At times, that block needs to be exploded for modification, then reblocked. PROBLEM: when the block is exploded, their reactors seem to be gone! Is there some way to deal with this, or am I hosed?!?

Check out this persons helpful library.
http://www.lee-mac.com/copyblock.html

when nothing is selected with ssget for arc and line they are still nil. You can't use sslength on a nil selection set.


This will default to: Mohan total of 0 Arc Object(s) & 0 Line Object(s) were converted to Polylines ...
if any arc or lines are converted it will update the 0 to that number.

---Edit
Might also want to limit your selection to model space or ctab (current tab). "_X" picks up any line or arc in the drawing even on other tabs but the command line pedit will only modify lines and arcs on current tab.

Thanks for sending this. I'll look into it soon.