I planned to included Imoen in my party the entire game, but wanted her to have better overall thieving skills since it is 99% likely she would be my party's only thief for the bulk of the game. So I planned to dual her to mage at 9th level thief rather than 7th level (as she is normally in SoA). That way I still get 4x back-stab plus another 50 points in theiving skills. Also, since I'm playing through BG, I used the Tome of Clear Thought (or whatever it is called) to raise her INT to 18. Solves 9th level spell issue.
I'm sure most if not all of you already see the problem. In all honesty, towards the end of ToSC, I just wanted to finish and get to SoA so I figured it would be easier & faster to just wait until SoA and dual to mage at the earliest opportunity. Yeah...I know.

While I could use ShadowKeeper, I'd rather try to find a "within the rules" type solution and I think I have one. I know BGT imports Imoen and other NPC in your party when you go to SoA "as is." Fortunately, I saved A LOT in BGI so it's not a big issue to go back and dual her to mage right after she reaches level 9 thief. I probably could get to mage level 5 or 6 by quickly replaying some of the remaining high XP quests. Even if her thieving skills are disabled, I think I can get to Yoshimo with a few memorized knock spells (if I don't die from all the traps

(1) If Imoen is "imported" to SoA via BGT already dual classed to mage, does she level up to 11th-13th level mage as she would in the standard, un-modded version of the game, or are her levels unchanged (i.e. same level when rescued as when she was captured)?
(2) If she does level up, does the game do this by setting her XP to some amount (thus she could be a level 1 mage when captured and still be 11th-13th when rescued), or does it add XP to her total when captured (thus if she's was level 4 or 5 when captured, she might be level 10 when rescued)?
I'm also curious as to what would happen if she was never dualed to mage, but left as a thief. Would she gain levels while at Spellhold or still be the same level as when you last saw her?
FWIW I tried to do an advanced forum search using search terms Imoen & Spellhold but got zero hits. Even just searching for Imoen nets zero hits for some reason. O.o
Any guidance/help is greatly appreciated.