Tunes are very easy to install. Steeda will load the SCT device with the custom tunes before they ship it. All you do is plug it into the OBD2 connector and follow the directions (super simple)... takes about 15 minutes for it to download/upload.
They can write a tune for whatever octane you want. The SCT holds 3 tunes, so they can write you 3 if desired. I had them write an 89 tune and 92 octane tune. 93 isn't real hard to find, but most stations have 92 around here. The Steeda tune keeps the knock sensors turned on, so if you have to use 91 octane with a 93 tune, its not going to be the end of the world.
When I bought mine, I asked about updated tunes when I add more goodies... I was told as long as I buy my performance parts from Steeda, they would be happy to send an updated tune.
Oh... and, its like driving a different car with a tune. Throttle response is amazing! You'll love it.