Hello, you called?
I customised a Blythe a few years ago and it was fun. I did everything except make the clothes and reroot her. Her name is Augenblick and I've put a couple of pictures in my gallery.
Anyhoo, customising Blythes can be a bit awkward and also expensive. I'm really, REALLY, lapsed in my knowledge and terms so I'll probably get some wrong here.
Mine is a Blythe Stardancer, customised. I picked her because I wanted long blonde hair, hate rerooting and at the time (I don't know if it's since changed) was built on the easiest to customise model (there were about three slightly different types at the time).
Mine's got replaced eyechips (there are 3 options for eyes), replaced pull string and charms, altered eye mech (repositioned and also altered so you can gently move her eyelids to stay at half-mast rather than just WIDE or CLOSED - I can't remember what it's called), some carving of eyes and lips, sand matt, MSC coat, full makeup makeover, replaced eyelashes, erm... I've probably forgotten something here.
They are quite fiddly to customise and I'd done a few different dolls before (I used to collect Pippas and BJDs). I nearly had a mental crisis trying to crack open her skull to change her eyes! The plastic feels so brittle compared to many dolls. The whole eye mech feels like it's about to break apart in your hands.
Still, I'd like to do another one some time, when I've had a think about what sort of look I want to go for. I'm kind of tied up in that respect at the moment - my friend got me a bunch of Monster High dolls to customise, but I just don't have the crafting room at the moment.
The best thing to do is join a forum because they're usually good for tips and info. Sadly, the one I used to go to is now defunct, but I just found this one:
blythekingdom.forumotion.com/
Seems to still be active, but looks like a PITA to join.