Programmatically, how to implement lichdom in BG2EE & EET?

[Endarire]

INTRO & FORENOTES
Greetings, all!

This post is about how, programatically, to implement lichdom in BG2EE & EET.  Specifically, I refer to the following aspects mentioned below.  (At present, I am not concerned about how lore-friendly this is.  In-game, Imoen can die and be revived freely without the world collapsing nor the plot ending.)

INTENDED STATS
Beyond the stats listed here except see invisibility, these are the notable mechanical features of my proposed version of lichdom:

-The lich's alignment becomes Evil.  Thus, LG & LN become LE; NG & TN become NE; and CG & CN become CE.

-The character's appearance does not change.  (This is done for the sake of simplicity.)  However, this character can use an innate ability to toggle the appearance change to be that of a normal lich, not a demilich.

-Unless the party is totally wiped out (that is, a TPK or total party kill), the lich will automatically revive after finishing an uninterrupted rest of at least 8 hours near to the party.  If this isn't feasible, then reviving the lich immediately after combat ends or a short amount of time passes is my preferred alternative.  (I know that by default in this edition of D&D, liches take longer to revive after being destroyed assuming their phylacteries are intact.)

OTHER QUESTIONS
-Upon achieving lichdom, should a character simply receive the Undead type and use the same opcodes as the ones a typical lich would have to obtain its immunities to certain status effects?

-For those importing characters between BG2EE's campaigns, how to ensure lichdom stays intact, and that, for example, a lich that dies in the final battle will be revived at the start of ToB?  I had considered forcibly reviving a dead lich at the end of SoA out of safety.

-If lichdom is only added to the BG2 part of the saga, what EET-specific special notes should I know about?

-As part of a quest to obtain lichdom, I intended to put a new unstealable quest item on various liches and demiliches - including named liches like Kangaxx - called 'lich dust.'  What's the best way to add this item en mass to these creatures' inventories?

FINALLY FOR NOW
Thankee!

Edited July 18, 2023 by Endarire