Amyd,
That is a good question. I have been looking into the specifics of FFS. Apparently, most of the competent surgeons in the USA would prefer that you have had hormone replacement and blocking for 1 to 2 years. There are some excellent resources on the internet, just enter FFS surgery. Some of the pictures show an amazing transformation, and significantly feminize a masculine face.
On the other hand, no one suggest that SRS is mandatory. I would think that Facial cosmetic surgery would be something you could get without undergoing SRS. . . Its certainly an interesting idea.
Strangely, there are surgeons who will give breast implants without SRS, as it is considered easily reversible.