I'd rather not.
The Yahg that existed canonically was a one-of-a-kind, and really should stay that way. I have no idea why someone would create a game that allowed for playable Yahg and no Batarians, that was pretty stupid. You guys might FIGHT a Yahg, or be tasked with stopping a gang of them from getting off-planet, but as their homeworld is currently under essentially a galactic quarantine it doesn't make sense to start drafting them into the Alliance.
But then, player characters are special and unique snowflakes, so if you really, really, really, really, REALLY wanna play a Yahg, I'll have to find some way to hide the fact that I basically just took them and scribbled out "yahg" to write "batarians".