Most platies and swordtails in the trade are already hybrids, so I wouldn't worry yourself on that score.
It's an odd thing, but female platies prefer males with swords, even though males of their own species don't have them!
It's thought that, for some unknown reason, the female ancestors of both species evolved a preferance for swords on tails, and the male swordtail was then 'bred' (not conciously, of course!)by the females to have swords, by choosing the males with the longest swords to mare with
The male platies never developed the mutation that gave them a sword, so they are without one, but the female platies stilll have that preference hidden away in their genes.
You can even make males more attractive to females by artifically lengthening the sword!