That seems to be the only way to go about it at the moment from what I have tried, though some gameplay elements can be a barrier to doing this (having a high enough reputation level to get them to accept the contract and enough cash to pay for the contract) and some customization options aren't available, most notably not being able to change their body type. I had hoped there might be another way, like maybe just being able to spawn a modded character into my roster, but guess this will work for now, thanks.
I have a similar issue, my game is set so that the population are mostly from one region, and so I was having trouble finding actors of a particular ethnicity from agencies. After trying out the plastic surgery menu with an actor I had under contract I found that I could change an actor's ethnicity using the Skin slider, but I also found that some of the options you get with the Eyes slider can change the ethnicity to Asian, which seems to overlap any ethnicity you get from changing their skin tone, so that's something to check for also if you find that it isn't changing their ethnicity tag.