Hi Mika,
I had no trouble after I travelled to Thailand in 2000 for my FFS. I came back with a surgeons letter stating I had facial surgery and was not even asked for it.
Remember that many people travel abroad for cosmetic surgery anyway. I went with my friend (a GG) when she had her face lift in 2008 and she came back wearing a support bandage and dark glasses for the bruising.
Major changes are not evident after FFS for many months as it takes time for swelling, bruising to go down. My jaw took over 10 months to heal.
However, I have just renewed my passport (which is a UK one) and now have a biometric passport, which includes face dimensions as the UK is introducing facial recognition software at passport control as part of standard passport checks (as an anti terrorism measure).
I dont think you will have any issues, just get a surgeons letter stating you had surgery.
Rebecca