You sound a bit confused.
Are you talking about black and white or colour reversal?
In the case of black and white, bleaching must be done before the re-exposure. If you do it afterwards you will have nice clear film.
In the case of colour, it can be done in either, but is usually done afterwards as part of the bleach-fix process.
What do you mean "fixing should not be necessary" ?
Fixing must be carried out after the second developer, otherwise you won't remove any unexposed or partially-exposed halides and your film will eventually fog.