Don't know about LA & Racial HD - I only used them in my local modules. Never played on a PW or other. Pure L40 build using the level up command.
The RWoT was a human only class. Probably still is. I leveled up in RWoT as a human, then used the PRC Leto to change the racial feat scripts and char model from human to Illithid. I also had to modify the stats with the dm commands. The 'shifted' bit was a narrative that in order to study in the human only class, the Illithid would have to shape shift into human form. Who else but a Betrayer would combine massive Mind Flayer racial intelligence with the RWoT + Archmage DC's & shift into a human to learn it?
The Frankenstein work was a fair PITA to execute, but a decent amount of fun in the end.
FYI, if you want to go the lich + demilich templates, apply the template before you change the racial scripts. Flayers are 'outsiders' and can't use the template for the EMT (Eternal Mind Thayer) build.
You may want to d-load the .bic files (base + lich template versions) and see if you think it would be fun. At least you can blast everything in your local modules.
On a PW, the best you can probably do is run a human, then get the lich template later. Note that the template boosts don't stack with items, so you'll have to make them permanent with PRC Leto or dm commands.