Depending on your interpretation of "regularly and deliberately", there is at least one race that qualifies:
Races of Faerun
The result of four noble houses of sun elves breeding with demons in an attempt to strengthen their bloodline, fey’ri are a type of planetouched that breeds true among their own kind. Marked by their fiendish blood, fey’ri are unique among most planetouched
in that they have a self-sustaining community, so they are raised among their own kind.
In addition, there are several races that are the result of interbreeding (Maeluth, Wispling, Alu-fiend, Cambion, etc.), however there is no direct evidence that these were deliberate and regular on the part of the mortal, rather than the fiend.