The Cure Will Not Influence the Breath
Cure light wounds targets a living creature:
...laying your hand upon a living creature, you channel...
Thus, unless the breath of life had already revived the target, CLW has no listed effect on dead creatures, only living or undead. In other words, BoL has to work on its own because CLW can't heal dead creatures, while BoL can. The CLW would not increase the damage threshold of BoL, because until the target is either alive or undead, CLW has no effect.
Using them together could net more healing, but only if BoL successfully revived the target.