Is there any hack for this?

[KnowitallSim]

You know, the really annoying glitch in OFB where people's faces change and they lose their eyebrows when you make them wear a uniform...

I tried searching and couldn't find a thing 

[J. M. Pescado]

This seems to be an unresolved hardcode glitch. Hacks can't directly fix it, and we don't have hard evidence on how consistently it appears.

[Zazazu]

It still happens in BV. But yeah, inconsistent. It's consistent for certain sims, but not for all sims.

[SnootCB]

The only thing that has worked for me is to go to the employee sims' homes and do a "change appearance" with the mirror (not actually changing their appearance, just hitting the check mark).  This obviously only works for playable employees.  And I think it only works when the employee is actually on the lot- changing their appearance when the employee is not on the business lot doesn't seem to have any effect.  I hope all that made sense.

[J. M. Pescado]

Try "fix flashing blue" on the Lot Debugger?

[pioupiou]

I use the fix flashing blue from he lot debugger (or any other handy mean to change appearance of a non controllable sim) with mixed success : sometimes it corrects the problem and sometimes it is only temporary (next time I play the business the sims wearing uniforms will revert to default face with no eye color and no eyebrows). I also have some sims that revert to another sim's face : for example : my sim Tara was fine when wearing her uniform on her business lot (community lot) when she was a YA. After graduating, each time she went to her business and wore (is that correct, I have some doubts, is it even an irregular verb ??) her uniform, her face reverted to her mother's face, complete with make-up and eye color. Change appearance only fixed it for this play session, the problem would come back after. When she aged to elder, she had a default face with no eyebrows and no eye color when wearing an uniform. After changing appearance a hundred times with no durable effect, it suddenly worked....
I have the same thing with some flashing blue accessories : I have currently a alien-vampire-zombie (legacy black sheep you know) and his teeth were always flashing blue upon re-entering the lot. I used fix flashing blue, regular mirror, fix appearance from Insim, fix tan&burn (lot debugger and insim), but the problem kept coming back... One day, I did nothing different, but it worked.... And since the vampire teeth are no longer flashing blue...
I'm dreaming of a fix as the blanck faces annoy me greatly...

[Gwill]

There is also something very weird with nannies and changing appearance.  Every time I've changed the look of a nanny they ended up with a blank face the first time; either completely missing, or a template 1, S1, no eyes, no eyebrow look.  Second time I make them over it works, but they end up with a double character file (N001_User00102.package and N001_User00102.1.package).
I only have the problem with nannies, but I've had it with ALL nannies.

[jsalemi]

After graduating, each time she went to her business and wore (is that correct, I have some doubts, is it even an irregular verb ??) her uniform, ...

Yup, that's right -- wore is the past tense of wear.

[pioupiou]

There is also something very weird with nannies and changing appearance.  Every time I've changed the look of a nanny they ended up with a blank face the first time; either completely missing, or a template 1, S1, no eyes, no eyebrow look.  Second time I make them over it works, but they end up with a double character file (N001_User00102.package and N001_User00102.1.package).
I only have the problem with nannies, but I've had it with ALL nannies.

You remind me : I have this same exact problem (change appearance make them revert to a blank face the first time I made them over, and they have 2 character files (but I did not pay attention whether the change appearance thing make the double character files appear or they ( double character files) exist even before attempting to change appearance)) with waiters, and I also notice that wolves (regular ones, not Leader of the pack) also have 2 character files, even if I don't remember changing their appearance. It was the case for regular stray wolves and adopted wolves (former strays).
Apart from the change appearance problem, they seem (waiters and wolves) to function normally... as far as I can tell...

Yup, that's right -- wore is the past tense of wear.

Thanks !! English classes are far away now, so my grammar is becoming rusty... (I'm french, and though I find english grammar incredibly easier than french grammar, I have lots of doubts when I write something...)

ETA : I think I also had this appearance problem and double character file with a streaker, but I'm not certain (and I'm not home to take a look at my files).

[Gwill]

It definitely caused the second character file in my case.  I was watching my character folder as I gave the nanny her makeover.