Acheron

Hm. I still think that 'exploitable, but only if you really tried to' is better than acting against the spell description (AKA the developers intent, since HLAs were already done 90% before my time anyway). I'm against playing at being the police.

Seems reasonable to me. Though it seems easy to stumble on the exploit by accident, I certainly didn't noticed it for several years using Refinements HLA's as a player with any number of mages and thieves (I admit that this may be in part because I don't take Scribe Scroll early in the HLA picks, and also that I use my scrolls that I scribe soon after creation in 95% of cases). I only discovered it while testing the kit I've been making which used a similar opcode.

As for Union, the immunity to spell failure seems like a good idea to me.
EDIT: You could also try to take advantage of opcode 280 and 281 to use a set wild magic effect to generate some interesting "metamagic" bonuses to casting. On the other hand this would break the wildmage's surging, allow a major abuse to Reckless Dweomer, and the effects may prove to be just too powerful for an ability with one hour duration (you could have spells cast at double level..., which is better than +5 but really doesn't do a lot except for dispel chances). If the WM were a class rather than a kit you could use eff files to fake  normal WM behavior (i.e. 5% of the rounds the aura is in affect the WM doesn't get the surge table set, but uses a random surge table). Also this would allow union to protect against the WM zones in WK. I'm not even that sure this will work, but I plan on experimenting with using 280 and 281 to make an HLA and will see, how it goes.

-Acheron/Starcrunch

A second issue:
The create scroll HLA uses opcode 122 to create the scrolls. This has a side effect that the scrolls only vanish after 12 hours in game if they are on the creature that created them. If Imoen creates a scroll and gives it to the PC, and the PC holds it until after the 3600 second timer expires, the scroll becomes permanent and will never vanish as intended.

Replacing opcode 122 with opcode 255 will solve this problem, though the scrolls will last 24 hours rather than 12 hours (it's not clear to me where the duration is set for this opcode, setting the duration to 0 nets me 24 hours then the item is destroyed no matter where it appears to be, IESDP indicates that the duration is in days; this is the opcode used for the Enchanted Weapon spell). If you wanted to keep the number of scrolls limited to no more than 6 at a time, you could reduce the number of times the Scribe Scroll can be chosen as an HLA to 2.

-Acheron/Starcrunch

I'm usually a caster of some kind.

When I took mostly BW parties:
BG1 - Imoen, Jaheira, Khalid, Dynaheir, Minsc. Xan often replaced Khalid or Minsc.

BG2 - Imoen, Jaheira, Arie, Keldorn or Har'Dalis, Cernd or Jan. Whether Keldorn and Cernd make it have a bit to do with how the PC sees the issue of family; Cernd is a bit bland but the truth is a quite like the bit of his personality you get to see, and I find having the shapeshifter to be a reasonably entertaining kit.

-Acheron/Starcrunch

I have lots, but a noteworthy one is Imoen's line to the imp in Watcher's Keep.

"I'm not sure whether to be impressed by your unshakeable devotion to duty, or appalled at your complete lack of initiative."

When does Imoen say this line. It's brilliant, one of my favorites (and it's appeared in other threads about quotes), but I can't ever remember it in game.

-Acheron/Starcrunch

Thank you!

-Starcrunch (or Acheron here at SHS)