[Fenris447]

For the record, I did get it figured out. I used the spell selector in the configurable thing, which imposes the hasagent tag on new copies of the spells. Then I searched all spells with that tag and built a list. That list was then used to find the spellbook and prepared versions of each of those spells.

All of this ran at Final 50000 and works perfectly.

  ~set our variables
  var searchexpr as string
  var otherexpr as string
  var blep as number

  ~start off the string for the tag expression with an open parenthesis
  searchexpr = "("

  ~look at all the spells that have been selected by this configurable   
  foreach pick in hero from BaseSpell where "hasagent.cfg5C1WthWrd"

  ~if this isn't the first spell we've found, add an OR (" | ") before it in the string
    if (blep > 0) then
      searchexpr &= " | " 
     endif

  ~add the found spell's thingid to the search expression
    searchexpr &= eachpick.tagids[thingid.?]

  ~blep tracks how many spells have been added to the list we're building
  ~so once we've found one, add to blep so we can add an OR as above
    blep += 1

  ~hide the found spell; this version of the spell is from the configurable
   perform eachpick.assign[Hide.Spell]
   nexteach

  ~close the tag expression string with a parenthesis
  searchexpr &= ")"

  ~make a copy the string with just the spells listed 
  otherexpr = searchexpr

  ~add the tag that shows we're looking for the spellbook version of the spell
  searchexpr &= " & portal.ClsBook"

  ~add the tag that shows we're looking for the prepared version of the spell
  otherexpr &= " & Helper.Memorized"


  ~run through the list of spells, looking for their spellbook versions
  foreach pick in hero from BaseSpell where searchexpr

  ~add "(Lost)" to the end of the spell's name
      eachpick.field[sNameMod].text = "Lost"

  ~hide this spell, as it's in the spellbook and has disappeared
      perform eachpick.assign[Hide.Spell]
  nexteach

  ~run through the list of spells, looking for their prepared versions
  foreach pick in hero from BaseSpell where otherexpr

  ~add "(Lost from spellbook)" to the end of the spell's name
      eachpick.field[sNameMod].text = "Lost from spellbook"
  nexteach