It's just a slight bump in clockspeeds applied to the VBIOS (at least that's my understanding). If, for whatever reason, you can't flash a nodded VBIOS you can always just bump the clocks up slightly on that card via PrecisionX or Afterburner should it not boost as high as the others.

like titan x  is at reference  settings / bios  a SC = S -upper C -locked   and may have a evga set bios  as in a factory overclocked card 
 
as you do know if the 2 or what ever  were SLI'ed   the cards will run in sli balanced out to the lesser cards specs  .    thing with a bios flash your not guaranteed that the reference card will take a SC bios  due to things as higher power states , ect..   . most times there binned cards tested to insure the card will take a factory OC  improved  bios  and run stable .
 
looks a ref titan x is clock 1000 boost 1075
titan x sc  is  clocked  1127 boost   1216
 
I overall real life you may never see that difference  anyway   unless you nit pick   maybe see 2 -7 fps ??
 
maybe as that one guy above said   use the non SC card in the first slot for /as  the primary card  and set the card with  afterburner  or per. x    to match the SC cards specs and try it and see  . sounds like your best bet / safest  over a bricking with a bad bios flash try ??   I don't think you going the outher way  getting the 2  non SC cards to stay at the 1 SC cards specs in SLI mode ??
 
 
 
 
may look at this
 
https://forums.evga.com/Titan-X-SC-Titan-X-nonSC-SLI-m2334504.aspx
then from sajins  link he posted ?
 
https://forums.evga.com/Titan-X-kboost-clocks-dont-stay-at-maximum-when-gaming-m2332974.aspx#2332974

that's the chance you take . it will work out or it don't
 
ijust don't see the difference between the cards to be a issue overall anyway   just a slight small gain if any at all

what was the end result? did you do it?